U.S. patent application number 14/332123 was filed with the patent office on 2014-11-06 for method and system for switching antenna and channel assignments in broadband wireless networks.
The applicant listed for this patent is Adaptix, Inc.. Invention is credited to Hui Liu, Manyuan Shen, Guanbin Xing.
Application Number | 20140328276 14/332123 |
Document ID | / |
Family ID | 36574141 |
Filed Date | 2014-11-06 |
United States Patent
Application |
20140328276 |
Kind Code |
A1 |
Xing; Guanbin ; et
al. |
November 6, 2014 |
METHOD AND SYSTEM FOR SWITCHING ANTENNA AND CHANNEL ASSIGNMENTS IN
BROADBAND WIRELESS NETWORKS
Abstract
A method and apparatus for antenna switching, grouping, and
channel assignments in wireless communication systems. The
invention allows multiuser diversity to be exploited with simple
antenna operations, therefore increasing the capacity and
performance of wireless communications systems. Channel
characteristics indicative of signal reception quality for downlink
or bi-directional traffic for each channel/antenna resource
combination are measured or estimated at a subscriber.
Corresponding channel characteristic information is returned to the
base station. Channel characteristics information may also be
measured or estimated for uplink or bi-directional signals received
at each of multiple receive antenna resources. The base station
employs channel allocation logic to assign uplink, downlink and/or
bi-directional channels for multiple subscribers based on channel
characteristics measured and/or estimated for the uplink, downlink
and/or bi-directional channels.
Inventors: |
Xing; Guanbin; (Issaquah,
WA) ; Shen; Manyuan; (Bellevue, WA) ; Liu;
Hui; (Clyde Hill, WA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Adaptix, Inc. |
Plano |
TX |
US |
|
|
Family ID: |
36574141 |
Appl. No.: |
14/332123 |
Filed: |
July 15, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12498924 |
Jul 7, 2009 |
8797970 |
|
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14332123 |
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11007064 |
Dec 7, 2004 |
7573851 |
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12498924 |
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Current U.S.
Class: |
370/329 |
Current CPC
Class: |
H04W 72/085 20130101;
H04W 48/16 20130101; H04W 72/04 20130101; H04B 17/382 20150115;
H04B 7/0613 20130101; H04W 72/0453 20130101; H04W 28/18 20130101;
H04B 17/24 20150115; H04L 27/261 20130101; H04L 5/06 20130101; H04B
7/0452 20130101; H04L 5/023 20130101 |
Class at
Publication: |
370/329 |
International
Class: |
H04L 5/06 20060101
H04L005/06; H04W 72/04 20060101 H04W072/04 |
Claims
1. A method for assigning a plurality of channels to support
communication between at least one subscriber and a base station in
a broadband wireless network, the method comprising: obtaining, at
the base station, at least one channel characteristic for each of
the plurality of channels hosted by each of a plurality of antenna
resources configured for communication on the plurality of
channels, the at least one channel characteristic indicative of
reception quality for a corresponding channel; and assigning, at
the base station, at least one of the plurality of channels to the
at least one subscriber based on the at least one channel
characteristic that is obtained, the obtaining of the at least one
channel characteristic being accomplished, at least in part, by
ranging operations performed by the at least one subscriber.
2. The method of claim 1, wherein the at least one of the plurality
of channels assigned includes one or more downlink channels for use
with transmissions sent from the base station to the at least one
subscriber.
3. The method of claim 1, wherein the at least one of the plurality
of channels assigned includes one or more uplink channels for use
with transmissions sent from the at least one subscriber to the
base station.
4. The method of claim 1, wherein the at least one of the plurality
of channels assigned includes one or more bi-directional link
channels employed for both uplink and downlink transmissions
between the base station and the at least one subscriber.
5. The method of claim 1, wherein the a east one channel
characteristic is measured by performing operations comprising:
broadcasting a respective beacon signal from each of the plurality
of antenna resources at the base station, each of the respective
beacon signals including transmissions over the plurality of
channels; measuring channel characteristics indicative of signal
quality for each of the plurality of channels at the at least one
subscriber; and sending data corresponding to the channel
characteristics indicative of signal quality that are measured from
the at least one subscriber to the base station.
6. The method of claim 5, wherein the respective beacon signals
that are broadcast from each of the plurality of antenna resources
includes orthogonal frequency division multiple access (OFDMA)
signals including OFDMA pilot symbols.
7. The method of claim 6, further comprising using, at the at least
one subscriber, information from pilot symbol periods and data
periods to measure channel and interference information.
8. The method of claim 6, wherein the OFDMA pilot symbols occupy an
entire orthogonal frequency division multiplexing (OFDM) frequency
bandwidth.
9. The method of claim 1, wherein the plurality of antenna
resources includes multiple individual antennas.
10. The method of claim 1, wherein at least one of the plurality of
antenna resources includes a set of antennas that are operated
collectively to perform at least one of transmit and receive radio
frequency transmissions.
11. The method of claim 1, wherein the broadband wireless network
supports OFDMA transmissions, and the plurality of channels include
combinations of OFDMA subchannels and antenna resources.
12. The method of claim 11, further comprising switching antennas
by adjusting inputs to fast Fourier transform (FFT) blocks in an
OFDMA transmitter module at a base-band.
13. The method of claim 11, wherein each of the at least one
subscriber is assigned to a single OFDMA channel, transmission for
the single OFDMA channel being provided by a single antenna
resource.
14. The method of claim 1, wherein the assigning of the at least
one of the plurality of channels is employed to assign respective
channels for downlink and uplink transmissions.
15. The method of claim 5, wherein the at least one channel
characteristic measurement includes at least one of
signal-to-interference plus noise ratio (SINR),
carrier-to-interference plus noise ratio (CINR), and
relative-signal strength indicator (RSSI) measurements.
16. The method of claim 5, wherein the at least one channel
characteristic measurement includes bit error rate (BER)
measurements.
17. The method of claim 5, wherein the at least one channel
characteristic measurement includes Quality of Service (QoS)
parameters.
18. The method of claim 1, wherein the plurality of channels
include at least one of channels and subchannels corresponding to
at least one of a frequency division multiple access (FDMA), time
division multiple access (TDMA), code division multiple access
(CDMA), orthogonal frequency division multiple access (OFDMA), and
space division multiple access (SDMA) channel schemes.
19. The method of claim 1, further comprising: obtaining,
periodically, updated channel characteristics for the at least one
subscriber; and reassigning at least one other channel for the at
least one subscriber in view of the updated channel
characteristics.
20. A method for assigning a plurality of channels in a broadband
wireless network, the method comprising: obtaining at least one
channel characteristic for each of the plurality of channels hosted
by at least one antenna resource of a plurality of antenna
resources configured for communication, the at least one antenna
resource being located at a base station, and the at least one
channel characteristic being indicative of reception quality of at
least one subscriber; determining, at the base station, an
available channel with the highest gain among the plurality of
antenna resources, the determining of the available channel being
based at least on one of the at least one channel characteristic
and a plurality of available channels of the at least one antenna
resource of the plurality of antenna resources; and assigning, at
the base station, at least one channel to the at least one
subscriber, the assigning of the at least one channel being based
at least on the determining of the available channel.
21. The method of claim 20, wherein obtaining of the at east one
channel characteristic comprises: measuring, at the at least one
subscriber, the at least one channel characteristic; and reporting
the at least one channel characteristic measured at the at least
one subscriber to the base station.
22. The method of claim 20, wherein the obtaining of the at least
one channel characteristic comprises: measuring, at the base
station, the at least one channel characteristic.
23. The method of claim 22, further comprising: receiving, at the
base station, test data for one or more uplink channels from the at
least one subscriber.
24. The method of claim 20, wherein the determining of the
available channel is performed for each of the at least one
subscriber in the assigning of the at least one channel.
25. The method of claim 20, further comprising: storing the
obtained at least one channel characteristic, the at least one
channel characteristic being updated on an ongoing basis; and
maintaining and updating the plurality of available channels of the
at least one antenna resource on an ongoing basis to provide
current channel allocation information.
26. The method of claim 20, wherein the determining of the
available channel comprises: selecting a channel of the plurality
of available channels with the highest gain for each of the
plurality of antenna resources; determining whether the selected
channel is available; selecting another channel of the plurality of
available channels with the next highest gain for each of the
plurality of antenna resources if the selected channel is not
available; comparing the gains of the selected channel and the
selected another channel; and selecting one of the selected channel
and the selected another channel with the highest gain for
assignment to the at least one subscriber in response to the
comparing of the gains of the selected channel and the selected
another channel.
27. A base station comprising: at least one antenna resource of a
plurality of antenna resources for communication over a wireless
communication system; a transmission module configured to generate
signals to transmit data over one of a downlink channel and a
bi-directional channel via the at least one antenna resource to at
least one subscriber; a reception module configured to: receive
data from signals at the at least one antenna resource; and extract
the data from the signals received at the at least one antenna
resource over one of an uplink channel and the bi-directional
channel from the at least one subscriber; and channel allocation
logic configured to: determine an available channel associated with
a highest gain among the plurality of antenna resources,
determination of the available channel being based on at least a
plurality of available channels of the at least one antenna
resource and at least one channel characteristic indicative of
reception quality for a corresponding channel obtained at the base
station; and assign at least one of the uplink channel, the
downlink channel, and the bi-directional channel to the at least
one subscriber, assignment of the at least one of the uplink
channel, the downlink channel, and the bi-directional channel being
based on at least the determination of the available channel.
28. The base station of claim 27, wherein the reception module is
further configured to receive the at least one channel
characteristic indicative of reception quality from the at least
one subscriber, the at least one subscriber being configured to
measure the at least one channel characteristic indicative of
reception quality.
29. The base station of claim 27, wherein the channel allocation
logic is further configured to measure the at least one channel
characteristic indicative of reception quality.
30. The base station of claim 29, wherein the reception module is
further configured to receive test data for the at least one uplink
channel from the at least one subscriber.
31. The base station of claim 27, further comprising: a channel
profile register configured to store the at least one channel
characteristics indicative of reception quality, the at least one
channel characteristics indicative of reception quality being
updated on an ongoing basis; and a channel assignment register
configured to maintain and update the plurality of available
channels of the at least one antenna resource on an ongoing basis
to provide current channel allocation information.
32. The base station of claim 27, wherein assignment of the least
one of the uplink channel, the downlink channel, and the
bi-directional channel to the at least one subscriber includes:
selection of a channel of the plurality of available channels with
the highest gain for each of the plurality of antenna resources;
determination of whether the selected channel is available;
selection of another channel of the plurality of available channels
with the next highest gain for each of the plurality of antenna
resources if the selected channel is not available; comparison of
the gains of the selected channel and the selected another channel;
and selection of one of the selected channel and the selected
another channel with the highest gain for assignment to the at
least one subscriber in response to the comparison of the gains of
the selected channel and the selected another channel.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation of U.S. patent
application Ser. No. 12/498,924 filed Jul. 7, 2009; which is a
Continuation of U.S. patent application Ser. No. 11/007,064 filed
Dec. 7, 2004 and issued Aug. 11, 2009 as U.S. Pat. No. 7,573,851;
the disclosure of which are expressly incorporated by reference
herein.
FIELD OF THE INVENTION
[0002] The present invention relates to the field of communications
systems; more particularly, the present invention relates to
techniques for switching channel and antenna assignments in
wireless networks.
BACKGROUND OF THE INVENTION
[0003] Spatial processing with antenna arrays is one of the most
used techniques in wireless communications. Among many schemes
developed to date, multiple-input multiple-output (MIMO) and
beamforming are often studied and have been proved to be effective
in increasing the capacity and performance of a wireless network
(see, e.g., Ayman F. Naguib, Vahid Tarokh, Nambirajan Seshadri, A.
Robert Calderbank, "A Space-Time Coding Modem for High-Data-Rate
Wireless Communications", IEEE Journal on Selected Areas in
Communications, vol. 16, no. 8, October 1998 pp. 1459-1478). On the
other hand, realization of MIMO or beamforming often means higher
complexity and cost on the system side. In particular, MIMO
operations entail complicated signal processing and decoding, while
beamforming involves hardware calibrations and multi-dimensional
data processing.
[0004] Over the years, orthogonal division multiple-access (OFDMA)
has become the access scheme of choice for almost all broadband
wireless networks (e.g., WiMAX, WiFi, and 4G cellular systems). In
OFDMA, multiple subscribers are allocated to different subcarriers,
in a fashion similar to frequency division multiple access (FDMA).
For more information, see Sari and Karam, "Orthogonal
Frequency-Division Multiple Access and its Application to CATV
Networks," European Transactions on Telecommunications, Vol. 9 (6),
pp. 507-516, November/December 1998 and Nogueroles, Bossert,
Donder, and Zyablov, "Improved Performance of a Random OFDMA Mobile
Communication System," Proceedings of IEEE VTC'98, pp.
2502-2506.
[0005] The fundamental phenomenon that makes reliable wireless
transmission difficult to achieve is time-varying multipath fading.
Increasing the quality or reducing the effective error rate in a
multipath fading channel may be extremely difficult. For instance,
consider the following comparison between a typical noise source in
a non-multipath environment and multipath fading. In environments
having additive white Gaussian noise (AWGN), it may require only 1-
or 2-db higher signal-to-noise ratio (SNR) using typical modulation
and coding schemes to reduce the effective bit error rate (BER)
from 10.sup.-2 to 10.sup.-3. Achieving the same reduction in a
multipath fading environment, however, may require up to 10 db
improvement in SNR. The necessary improvement in SRN may not be
achieved by simply providing higher transmit power or additional
bandwidth, as this is contrary to the requirements of next
generation broadband wireless systems.
[0006] Multipath phenomena causes frequency-selective fading. In a
multiuser fading environment, the channel gains are different for
different subcarriers. Furthermore, the channels are typically
uncorrelated for different subscribers. This leads to a so-called
"multiuser diversity" gain that can be exploited through
intelligent subcarrier allocation. In other words, it is
advantageous in an OFDMA system to adaptively allocate the
subcarriers to subscribers so that each subscriber enjoys a high
channel gain. For more information, see Wong et al., "Multiuser
OFDM with Adaptive Subcarrier, Bit and Power Allocation," IEEE J.
Select. Area Commun., Vol. 17(10), pp. 1747-1758, October 1999.
[0007] Within one cell, the subscribers can be coordinated to have,
different subcarriers in OFDMA. The signals for different
subscribers can be made orthogonal and there is little intracell
interference. However, with an aggressive frequency reuse plan,
e.g., the same spectrum is used for multiple neighboring cells, the
problem of intercell interference arises. It is clear that the
intercell interference in an OFDMA system is also frequency
selective and it is advantageous to adaptively allocate the
subcarriers so as to mitigate the effect of intercell
interference.
[0008] One approach to subcarrier allocation for OFDMA is a joint
optimization operation, not only requiring the activity and channel
knowledge of all the subscribers in all the cells, but also
requiring frequent rescheduling every time an existing subscribers
is dropped off the network or a new subscribers is added onto the
network. This is often impractical in real wireless system, mainly
due to the bandwidth cost for updating the subscriber information
and the computation cost for the joint optimization.
[0009] Existing approaches for wireless traffic channel assignment
are subscriber-initiated and single-subscriber (point-to-point) in
nature. Since the total throughput of a multiple-access network
depends on the channel fading profiles, noise-plus-interference
levels, and in the case of spatially separately transceivers, the
spatial channel characteristics, of all active subscribers,
distributed or subscriber-based channel loading approaches are
fundamentally sub-optimum. Furthermore, subscriber-initiated
loading algorithms are problematic when multiple transceivers are
employed as the base-station, since the
signal-to-noise-plus-interference ratio (SINR) measured based on an
omni-directional sounding signal does not reveal the actual quality
of a particular traffic channel with spatial processing gain. In
other words a "bad" traffic channel measured at the subscriber
based on the omni-directional sounding signal may very well be a
"good" channel with proper spatial beamforming from the
base-station. For these two reasons, innovative information
exchange mechanisms and channel assignment and loading protocols
that account for the (spatial) channel conditions of all accessing
subscribers, as well as their QoS requirements, are highly
desirable. Such "spatial-channel and QoS-aware" allocation schemes
can considerably increase the spectral efficiency and hence data
throughput in as given bandwidth. Thus, distributed approaches,
i.e., subscriber-initiated assignment are fundamentally
sub-optimum.
SUMMARY OF THE INVENTION
[0010] A method and apparatus is disclosed herein for antenna
switching and channel assignments in wireless communication
systems. Channel characteristics indicative of signal reception
quality are obtained for each of multiple channels hosted by each
antenna resource at a base station. Channels are assigned to
subscribers based on the channel characteristics, base station,
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The present invention will be understood more fully from the
detailed description given below and from the accompanying drawings
of various embodiments of the invention, which, however, should not
be taken to limit the invention to the specific embodiments, but
are for explanation and understanding only.
[0012] FIG. 1 shows a base station employing a pair of switched
antennas that are used to communicate with various subscribers,
wherein each subscriber is assigned to a channel corresponding to a
respective subchannel/antenna combination.
[0013] FIG. 2 shows an OFDMA subchannel allocation for the
subscribers shown in FIG. 1 prior to the entry of a new
subscriber.
[0014] FIG. 3a shows a beacon signal sent out by each of the
antennas in FIG. 1 that is received by a new subscriber and
contains various channels via which the new subscriber can measure
downlink or bi-directional link channel characteristics that are
returned to the base station.
[0015] FIG. 3b shows a ranging signal sent out by the new
subscriber and containing test data sent over various channels via
which uplink or bi-directional channel characteristics can be
measured at each of the switched antennas of FIG. 1.
[0016] FIG. 4a is a flowchart illustrating operations performed to
obtain downlink or bi-directional link channel characteristics
using the beacon signal scheme of FIG. 3a.
[0017] FIG. 4b is a flowchart illustrating operations performed to
obtain uplink or bi-directional link channel characteristics using
the ranging signal scheme of FIG. 3b.
[0018] FIG. 5 depicts exemplary subscriber's channel responses
corresponding to channel characteristics for the switched antennas
of FIG. 1.
[0019] FIG. 6 shows a flowchart illustrating operations performed
to assign channels to various users for a base station having
multiple antenna resources, wherein a channel comprising the best
available subchannel/antenna combination is assigned to a new user
based on measured or estimated subchannel characterstics for each
antenna.
[0020] FIG. 7 is a block diagram of one embodiment of an OFDMA/SDMA
base-station.
[0021] FIG. 8 shows an architecture for a OFDMA transmitter module
employing multiple switched antennas.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
[0022] The marriage of OFDMA and spatial processing provides
powerful platform for multiuser broadband communications. The
present invention describes a method, apparatus, and system for
easy integration of OFDMA with antenna arrays of various
configurations. The method and apparatus allows multiuser diversity
to be exploited with simple antenna operations, therefore
increasing the capacity and performance of wireless communications
systems. In one embodiment, Channel characteristics indicative of
signal reception quality for downlink or bi-directional traffic for
each channel (e.g., OFDMA subchannel/antenna resource combination)
are measured or estimated at a subscriber. Corresponding channel
characteristic information is returned to the base station. Channel
characteristics information may also be measured or estimated for
uplink or bi-directional signals received at each of multiple
receive antenna resources. The base station employs channel
allocation logic to assign uplink, downlink and/or bi-directional
channels for multiple subscribers based on channel characteristics
measured and/or estimated for the uplink, downlink and/or
bi-directional channels.
[0023] The benefits of the present invention include simpler
hardware (much less expensive than beamforming antenna arrays) and
easier processing (much less complicated than MIMO), without
sacrificing the overall system performance. In addition to OFDMA
implementation, the general principles ay be utilized in FDMA
(frequency division multiple access), TDMA (time division multiple
access), CDMA (code division multiple access), OFDMA, and SDMA
(space division multiple access) schemes, as well as combinations
of these multiple-access schemes.
[0024] In the following description, numerous details are set forth
to provide a more thorough explanation of the present invention. It
will be apparent, however, to one skilled in the art, that the
present in tendon may be practiced without these specific details.
In other instances, well-known structures and devices are shown in
block diagram form, rather than in detail, in order to avoid
obscuring the present invention.
[0025] Some portions of the detailed descriptions which follow are
presented in terms of algorithms and symbolic representations of
operations on data bits within a computer memory. These algorithmic
descriptions and representations are the means used by those
skilled in the data processing arts to most effectively convey the
substance of their work to others skilled in the art. An algorithm
is here, and generally, conceived to he a self-consistent sequence
of steps leading to a desired result. The steps are those requiring
physical manipulations of physical quantities. Usually, though not
necessarily, these quantities take the form of electrical or
magnetic signals capable of being stored, transferred, combined,
compared, and otherwise manipulated. It has proven convenient at
times, principally for reasons of common usage, to refer to these
signals as bits, values, elements, symbols, characters, terms,
numbers, or the like.
[0026] It should be borne in mind, however, that all of these and
similar terms are to be associated with the appropriate physical
quantities and are merely convenient labels applied to these
quantities. Unless specifically stated otherwise as apparent from
the following discussion, it is appreciated that throughout the
description, discussions utilizing terms such as "processing" or
"computing" or "calculating" or "determining" or "displaying" or
the like, refer to the action and processes of a computer system,
or similar electronic computing device, that manipulates and
transforms data represented as physical (electronic) quantities
within the computer system's registers and memories into other data
similarly represented as physical quantities within the computer
system memories or registers or other such information storage,
transmission or display devices.
[0027] The present invention also relates to apparatus for
performing the operations herein. This apparatus may be specially
constructed for the required purposes, or it may comprise a
general-purpose computer selectively activated or reconfigured by a
computer program stored in the computer. Such a computer program
may be stored in a computer readable storage medium, such as, but
is not limited to, any type of disk including floppy disks, optical
disks, CD-ROMs, and magnetic-optical disks, read-only memories
(ROMs), random access memories (RAMs), EPROMs, EEPROMs, magnetic or
optical cards, or any type of media suitable for storing electronic
instructions, and each coupled to a computer system bus.
[0028] The algorithms and displays presented herein are not
inherently related to any particular computer or other apparatus.
Various general-purpose systems may be used with programs in
accordance with the teachings herein, or it may prove convenient to
construct more specialized apparatus to perform the required method
steps. The required structure for a variety of these systems will
appear from the description below. In addition, the present
invention is not described with reference to any particular
programming language. It will be appreciated that a variety of
programming languages may be used to implement the teachings of the
invention as described herein.
[0029] A machine-readable medium includes any mechanism for storing
or transmitting information in a form readable by a machine (e.g.,
a computer). For example, a machine-readable medium includes read
only memory ("ROM"); random access memory ("RAM"); magnetic disk
storage media; optical storage media; flash memory devices;
electrical, optical, acoustical or other form of propagated signals
(e.g., carrier waves, infrared signals, digital signals, etc.);
etc.
Overview
[0030] Efficient exploitation of spatial diversity in a highspeed
wireless network is a challenging task due to the broadband nature
of spatial channel characteristics. In OFDMA networks, the wide
spectrum is partitioned into parallel narrowband traffic channels
(commonly referred to as "sub-channels"). The methodology described
herein, provides a means for allocating traffic channels-through
intelligent traffic channel assignment.
[0031] In the communication system described herein, channel
allocation logic performs "channel-aware" traffic channel
allocation. In one embodiment, the channel allocation logic
provides bandwidth on demand and efficient use of spectral
resources (e.g., OFDMA traffic channels) and spatial resources
(e.g., the physical location of subscribers as it pertains to
spatial beamforming) and performs traffic channel assignment based
on broadband spatial channel characteristics of a requesting
subscriber and on-going subscribers. Furthermore, channels are
allocated to subscribers based on the best antenna resources for
those subscribers. Thus, the channel allocation provides enhanced
performance over a larger number of subscribers than might be
typically obtained using conventional channel assignment
approaches.
[0032] In responding to a link request from a new subscriber, or
when the base-station has data to transmit to a standby subscriber,
the logic first estimates the channel characteristics of
transmissions received over all, or a selected portion of OFDMA
traffic channels for each antenna resource. As used herein, an
antenna resource may comprise a single antenna, or a sub-array of
antennas (from an array of an antennas for a given base station)
that are collectively used to transmit and/or receive signals from
subscribers. For example, multiple antennas may be configured to
function (effectively) as a single antenna resource with improved
transmission characteristics (when compared with a single antenna)
by using one or more signal diversity schemes (spatial, frequency,
and/or time). In one embodiment, the channel characteristics, along
with channel assignment for on-going subscribers are used to
determine which antenna resource is optimum for each subscriber.
The channel characteristic data may be stored in a register or
other type of storage location (e.g., a database, file, or similar
data structure). In one embodiment, traffic channels corresponding
to antenna resources that have the best communication
characteristics are assigned to the accessing subscriber to satisfy
the service request of the accessing subscriber.
[0033] An exemplary portion of a broadband wireless network 100
including a base station 102 that implements the channel selection
techniques described herein is shown in FIG. 1. Base station 102
includes facilities to support communication with various
subscribers, as depicted by a mobile (phone) subscribers 104 and
106, fixed (location) subscribers 108 and 110, and a mobile (PDA)
subscriber 112. These facilities include a receive module 114, a
transmit module 116, and channel management component 118, as well
as antennas 120A (also referred to herein as antenna #1) and 120B
(also referred to herein as antenna #2).
[0034] Generally, a base station communicates with a subscriber in
the following manner. Data bursts, such as cellular packets, IP
packets or Ethernet frames, are encapsulated into an appropriate
data frame format (e.g., IEEE 802.16 for WiMAX networks) and
forwarded from a network component, such as a ratio access node
(RAN), to an appropriate base station within a given cell. The base
station then transmits to a selected subscriber (identified by the
data frame) using a unidirectional wireless link, which is referred
to as a "downlink." Transmission of data from a subscriber to
network 100 proceeds in the reverse direction. In this case, the
encapsulated data is transmitted from a subscriber to an
appropriate base station using a unidirectional wireless link
referred to as an "uplink." The data packets are then forwarded to
an appropriate RAN, converted to IP Packets or Ethernet frames, and
transmitted henceforth to a destination node in network 100. Under
some types of broadband wireless networks, data bursts can be
transmitted using either Frequency-Division-Duplexing (FDD) or
Time-Division-Duplexing (TDD) schemes. In the TDD scheme, both the
uplink and downlink share the same RF (radio frequency) channel,
but do not transmit simultaneously, and in the FDD scheme, the
uplink and downlink operate on different RF channels, but the
channels may be transmitted simultaneously. In general, the
unidirection wireless downlinks may comprise a point-to-point (PP)
link, a point-to-multiple (PMP), or a MIMO link. Uplinks typically
comprise PP or PMP links, although MIMO links may also be used.
[0035] Multiple base stations are configured to form a
cellular-like wireless network, wherein one or more base stations
may be accessible to a given subscriber at any given location using
a shared medium (space (air) through which the radio waves
propagate). A network that utilizes a shared medium requires a
mechanism to efficiently share it. Sharing of the air medium as
enabled via an appropriate channel-based scheme, wherein respective
channels are assigned to each subscriber within the access range of
a given base station. Typical channel-based transmission schemes
include FDMA, TDMA, CDMA, OFDMA, and SDMA, as well as combination
of these multiple access schemes. Each of these transmission
schemes are well-known in the wireless networking arts.
[0036] To facilitate downlink and uplink communications with the
various subscribers, base station 102 provides multiple antennas.
For illustrative purposes, these are depicted as antenna 120A and
antenna 120B (antennas #1 and #2) in FIG. 1. Signals from two or
more of the multiple antennas may be combined to support beam
forming or spatial multiplexing, or may be used individually for
different groups of subscribers using well-known techniques. The
multiple antennas may also be configured in one or more clusters.
In general, antennas 120A and 120B are representative of various
antenna types employed in wireless broadband network, including
sectorized antennas and omni-directional antennas.
[0037] Under one embodiment, each subscriber is assigned to a
respective channel or subchannel provided by one of the antennas at
a given base station (or antenna resources, when multiple antennas
may be combined to transmit or receive signals). For example, in
the illustrated configuration of FIG. 1, mobile subscriber 104 and
fixed subscriber 110 are assigned to respective channels
facilitated by antenna 120A, while fixed subscriber 108, and mobile
subscribers 106 and 112 are assigned to respective channels
facilitated by antenna 120B. As described in further detail below,
the channel/antenna or subchannel/antenna selection for each
subscriber is based on the best available channel characteristics
at the point at which a new subscriber enters the network via a
given base station (e.g., base station 102). In addition, channels
may be re-assigned to on-going subscribers based on changes in
measured channel characteristics.
[0038] By way of illustration, the following discussion concerns
allocation of channels for an OFDMA network. However, this is not
meant to be limiting, as similar principles may be applied to
wireless networks employing other channel-based transmission
schemes, including FDMA, TDMA, CDMA, SDMA, and OFDMA/SDMA, as well
as other combinations of these schemes.
[0039] In accordance with aspects of the present invention, a
channel allocation scheme is now disclosed that ate downlink and/or
uplink or shared (bi-directional) channels for respective
subscribers to selected antenna resources based on current channel
characteristics. The overall approach is to assign channel/antenna
or subchannel/antenna combinations having the best channel
characteristics to new and on-going subscribers.
[0040] FIG. 2 shows an exemplary set of initial OFDMA channel
assignments for the various subscribers shown in FIG. 1. In the
illustrated embodiment, each of antennas #1 and #2 (120A and 120B)
supports N subchannels. Typically, a respective subchannel for a
given antenna or antenna resource is assigned to each subscriber.
In some cases, multiple subchannels may be assigned for the same
subscriber. For illustrative purposes, only a single set of
subchannel assignments in FIG. 2 are shown, wherein the single set
is illustrative of uplink, downlink, or shared (same channel for
uplink and downlink) channel assignments. It will be understood
that another set of channel assignments will also exist for
transmission schemes that employ separate channels for downlink and
uplink traffic.
[0041] Referring to FIGS. 1 and 3a, now suppose that a new mobile
subscriber 122 attempts to initiate service with base station 102,
either by originating a new service request or in connection with a
hand-over from another (currently) serving base station (not shown)
to base station 102. As discussed above, it is desired to assign a
best available channel to the new user. Accordingly, a mechanism
for determining the best available channel is provided.
[0042] With further reference to the flowchart of FIG. 4a, one
embodiment of a process for determining the channel characteristics
begins at a block 400, wherein a base station broadcasts a beacon
signal covering all sub-channels over the frequency bandwidth
allocated to that station from each of its antenna resources. For
example, under an FDMA scheme, the broadcast signal may comprise a
signal that varies in frequency over the allocated bandwidth using
a pre-determined cycle. Under a CDMA scheme, a test signal
transmitted over various CDMA channels that are changed in a cyclic
manner may be used. Under a channel scheme that supports multiple
channels operating on the same frequencies (such as OFDMA), the
broadcast signal will include applicable sub-channel/frequency
combination per antenna resource. (Further details of one
embodiment of an OFDMA beacon signal scheme are described below).
As a result, the broadcast beacon signal will provide information
from which spatial and frequency channel characteristics may be
determined. In one embodiment, the beacon signal is broadcast over
a management channel on an ongoing basis. In the case of some
channel schemes based on time slots (e.g., OFDMA, CDMA, TDMA), it
may be necessary to first perform timing synchronization between a
base station and subscriber to enable the subscriber to adequately
tune into (e.g., synchronize with) the broadcast beacon signal.
[0043] In response to the beacon signal, the subscriber (device)
tunes its receiving unit to cycle through the various channels (in
synchrony with the channel changes in the beacon signal) while
measuring channel characteristics. For example, in one embodiment,
signal-to-interference plus noise ratio (SINR, also commonly
referred to as carrier-to-interference plus noise ratio (CINR) for
some types of wireless networks) and/or relative-signal strength
indicator (RSSI) measurements are performed at the subscriber to
obtain the channel characteristic measurements or estimates. In one
embodiment, the channel characteristic measurement pertains to data
rates that can reliably be obtained for different channels, as
exemplified by the sets of channel characteristic measurement data
corresponding to antennas #1 and #2 shown in FIG. 5 (with reduced
versions shown in FIG. 3a). For example, it is common to measure
such data rates in Bits per second per Hertz (Bit/s/Hz) as shown in
FIG. 5. In another embodiment, BER measurements are made for each
channel/antenna resource combination. In yet another embodiment,
Quality of Service (QoS) parameters, such as delay and jitter are
measured to obtain the channel characteristic data. In still other
embodiments, various indicia of signal quality/performance may be
measured and/or estimated to obtain the channel characteristic
data.
[0044] Continuing at a block 404 in FIG. 4a, after, or as channel
characteristic measurements are taken, corresponding data is
returned to the base station. In one embodiment, this information
is returned via a management channel employed for such purposes. In
response, a best available channel is selected to be assigned to
the subscriber in view of current channel availability information
and the channel characteristic data. Details of the selection
process are described below with reference to FIG. 6.
Exemplary OFDMA Downlink/Bi-Directional Link Channel
Characterization
[0045] Under one embodiment employed for OFDMA networks, each base
station periodically broadcasts pilot OFDM symbols to every
subscriber within its cell (or sector). The pilot symbols, often
referred to as a sounding sequence or signal, are known to both the
base station and the subscribers. In one embodiment, each pilot
symbol covers the entire OFDM frequency bandwidth. The pilot
symbols may be different for different cells (or sectors). The
pilot symbols can serve multiple purposes: time and frequency
synchronization, channel estimation and SINR measurement for
subchannel allocation.
[0046] In one embodiment, each of multiple antenna resources
transmits pilot symbols simultaneously, and each pilot symbol
occupies the entire OFDM frequency bandwidth. In one embodiment,
each of the pilot symbols have a length or duration of 128
microseconds with a guard time, the combination of which is
approximately 152 microseconds. After each pilot period, there are
a predetermined number of data periods followed by another set of
pilot symbols. In one embodiment, there are four data periods used
to transmit data after each pilot, and each of the data periods is
152 microseconds in length.
[0047] As the pilot OFDM symbols are broadcast, each subscriber
continuously monitors the reception of the pilot symbols and
measures (e.g., estimates) the SINR and/or other parameters,
including inter-cell reference and intra-cell traffic, for each
subchannel. In one embodiment, the subscriber first estimates the
channel response, including the amplitude and phase, as if there is
no interference or noise. Once the channel is estimated, the
subscriber calculates the interference/noise from the received
signal.
[0048] During data traffic periods, the subscribers can determine
the level of interference again. The data traffic periods are used
to estimate the intra-cell traffic as well as the subchannel
interference level. Specifically, the power difference during the
pilot and traffic periods may be used to sense the (intra-cell)
traffic loading and inter-subchannel interference to select the
desirable subchannel.
[0049] In one embodiment, each subscriber measures the SINR of each
subchannel (or a set of subchannels corresponding to available
subchannels) and reports these SINR measurements to their base
station through an access channel. The feedback of information from
each subscriber to the base station contains an SINR value (e.g.,
peak or average) for each subchannel. A channel indexing scheme may
be employed to identify the feedback data for each subchannel; no
indexing is needed if the order of information in the feedback is
known to the base station in advance.
[0050] Upon receiving the feedback from a subscriber, the base
station selects a subchannel to assign to the subscriber in a
manner similar to that described below. After subchannel selection,
the base station notifies the subscriber about the subchannel
assignment through a downlink common control channel or through a
dedicated downlink traffic channel if the connection to the
subscriber has already been established. In one embodiment, the
base station also informs the subscriber about the appropriate
modulation/coding rates. Once the basic communication link is
established, each subscriber can continue to send the feedback to
the base station using a dedicated traffic channel (e.g., one or
more predefined uplink access channels).
[0051] The foregoing scheme determines channel characteristics for
downlink and shared bi-directional link channels. However, it may
be inadequate for predicting uplink channel characteristics. The
reason for this is that multipath fading is generally
unidirectional. As a result, a channel that produces good downlink
channel characteristics (as measured at a receiving subscriber) may
not provide good uplink channel characteristics as measured at a
receiving base station).
[0052] With reference to FIGS. 3b and 4b, one embodiment of a
process for determining channel characteristics for uplink channels
(or optionally, bi-directional shared channels) begins at a block
450 (FIG. 4b), wherein a subscriber performs ranging with each
antenna resource at the base station. The term "ranging" is used by
the WiMAX (IEEE 802.16) standard to define a set of operations used
by a subscriber station to obtain service availability and signal
quality information from one or more base stations. During this
process, a subscriber station synchronizes with a base station and
a series of messages are exchanged between the subscriber station
and the base station. Also, signal quality measurements may be
obtained by performing CINR and/or RSSI measurements at the base
station and/or the subscriber station.
[0053] As used herein, "ranging" generally concerns transmission
activities initiated by a subscriber to enable uplink channel
characteristics to be measured by a base station thus, ranging
includes the aforementioned ranging operations defined by the WiMAX
specification for WiMAX networks, as well as other techniques used
to obtain uplink channel characteristics. For example, similar
operations to those employed during WiMAX ranging may be employed
for other types of broadband wireless networks. In one embodiment a
subscriber and base station exchange information relating to a
channel sequence over which channel characteristic measurements
will be made. For example, in some implementations a base station
may only identify unused uplink channels to measure, thus reducing
the number of measurements that will be performed. Optionally, the
channel sequence may be known in advance.
[0054] Continuing at a block 452, in view of the channel sequence
information, the subscriber cycles through the applicable uplink
channels while transmitting test data to each base station antenna
resource. In general, this may be performed concurrently for all
individual antennas or combined antenna resources, or may be
perforated separately for each antenna resource. In connection with
the transmission of the test data via each uplink channel, channel
characteristic measurements are made by the base station in block
452 and stored in block 454. In general, the channel characteristic
measurements performed in block 452 are analogous to those
performed in block 402 (FIG. 4a), except now the measurements are
made at the base station rather than at the subscriber. The best
available uplink channel to assign the subscriber is then selected
in a block 456 in the manner now described with reference to the
operations of FIG. 6.
[0055] In further detail, FIG. 6 depicts a process for channel
assignment under a generic configuration for a base station having
a variable number of users (subscribers), antennas (individual
antennas or combined antenna resources), and subchannels for each
antenna or combined antenna resource. Accordingly, a set of data
600 comprising an initial input defining the number be of users,
antennas, number of subchannels, and maximum number of subchannels
per antenna is provided to the processing operations depicted below
data 600 in FIG. 6.
[0056] As depicted by start and end loop blocks 602 and 612, the
operations depicted in the blocks 604, 606, and 610 are performed
for each of users 1 to P. First, in block 604, the available
subchannel with the highest gain is selected among all available
antennas (or combined antenna resources, if applicable). As
depicted by input data block 606, the set of available subchannels
for each of antennas is maintained and updated on an ongoing basis
to provide current subchannel allocation information to block 604.
In addition, channel characteristic profile data measured in blocks
402 and/or 452 (as applicable) is stored in a subscribers channel
profile register 608 and updated on an ongoing basis. During
channel selection for a particular subscriber, corresponding
channel characteristic profile data is retrieved from subscribers'
channel profile register 60 as an input to block 604.
[0057] In view of input data from data blocks 606 and 60S, a
subchannel k and antenna j are assigned to the user i in block 610.
The process then moves to the next user (e.g., user i+1) to assign
a channel comprising a subchannel/antenna combination for that user
via the operations of block 604 in view of updated input data from
data blocks 606 and 608. In general, these operations are repeated
on an ongoing basis.
[0058] These concepts may be more clearly understood from exemplary
channel assignment parameters in accordance with network
participants shown in the figures herein. For example, FIG. 2
illustrates an initial condition wherein mobile subscriber 106 and
fixed subscriber 110 are respectively assigned channels comprising
subchannels 1 and 6 for antenna #1, while fixed subscriber 108 is
assigned a channel comprising subchannel 2 for antenna #2 and
mobile subscribers 104 and 112 are respectively assigned channels
comprising subchannels 5 and M-1 for antenna #2. For point of
illustration, these channel assignments are representative of
uplink, downlink, or bi-directional link channel assignments. For
the following example it is presumed that corresponding channel
assignment information is present in data block 606.
[0059] Now suppose that mobile subscriber 122 (FIGS. 1 3a, and 3b)
attempts to enter the network. First, channel characteristic
measurement data will be collected in accordance with the
operations of the flowcharts shown in FIGS. 4a and/or 4b, as
applicable. This will update subscribers' channel profile register
608. During the processing of block 604, antenna channel
characteristic data for each of antennas #1 and #2 will be
retrieved from subscribers' channel profile register 608. As
discussed above, exemplary channel characteristic data are depicted
in FIG. 5. In view of this channel characteristic data in
combination with available subchannel information shown in FIG. 2
and retrieved from data block 606, a new channel for mobile
subscriber 122 is selected in block 610.
[0060] In the view of the exemplary channel characteristic data and
subchannel assignment data in respective FIGS. 5 and 2, subchannel
3 for antenna #2 should be assigned to mobile subscriber 122, which
represents the available channel with the highest gain (e.g.,
available channel with the best channel characteristics). In one
embodiment, this may be determined in the following manner. First,
the channel with the highest gain is selected for each antenna
resource. In the present example, this corresponds to channel 1 for
antenna #1 and subchannel 3 for antenna #2. Next, a determination
is made to whether that subchannel is available. In the case of
subchannel 1 for antenna #1, this subchannel is already assigned,
so it is not available. The channel corresponding to the next best
gain is then selected for antenna #1, which corresponds to
subchannel 5. Likewise, a similar determination is made for channel
2. In the present example, subchannel 3, which represents the
subchannel for antenna #2 with the highest gain, is available. The
gains for subchannel 5 for antenna #1 and subchannel 3 for antenna
#2 are then compared. The subchannel/antenna combination with the
highest gain is then selected for assignment to the new subscriber.
This results in the selection of subchannel 3 for antenna #2 as the
new channel to be assigned to mobile subscriber 122.
[0061] From time to time, processing logic may perform channel
reassignment by repeating the process described above with
reference to FIG. 6. This channel reassignment compensates for
subscriber movement and any changes in interference. In one
embodiment, each subscriber reports its channel characteristics
data. The base station then performs selective reassignment of
subchannel and antenna resources. That is, in one embodiment some
of the subscribers may be reassigned to new channels, while other
channel assignments will remain as before. In one embodiment,
retraining is initiated by the base station, and in which ease, the
base station requests a specific subscriber or subscribers to
report its updated channel characteristics data. A channel
reassignment request may also be submitted by a subscriber when it
observes channel deterioration.
[0062] FIG. 7 is a block diagram of base station 700 that
communicates with multiple subscribers through OFDMA and spatial
multiplexing. The base-station 700 comprises receiving antenna
array 702, a receiver module 703 including a set of down-converters
704 coupled to receiving antenna array 700 and an OFDM demodulator
706, a channel characteristics module 708, an on-going traffic
register 710, OFDMA subchannel channel allocation logic 712, a
subscribers's channel profile register 608, an OFDMA medium access
controller (MAC) 714, an OFDM modem 716, a beacon signal generator,
an OFDMA transmitter module 718 including a sub-channel formation
block 720, and a set of up-converters 722 that provide inputs to
respective antenna resources in a transmission antenna array
724.
[0063] Uplink signals, including the accessing signal from a
requesting subscriber, are received by receiving antenna array 702
and down-converted to the base-band by down-converters 704. The
base-baud signal is demodulated by OFDM demodulator 706 and also
processed by channel characteristics block 708 for estimation of
the accessing subscriber's uplink channel characteristics using one
of the techniques described above or other well-known signal
quality estimation algorithms. The estimated or measured channel
characteristics data, along with channel characteristics
corresponding to channels assigned to ongoing traffic that is
stored in subscribers channel profile register 608 and on-going
traffic information stored in the on-going traffic register 710,
are fed to OFDMA subchannel allocation logic 712 to determine a
channel assignment for the accessing subscriber, and possibly
partial or all of the on-going subscribers. The results are sent to
OFDMA MAC 714, which controls the overall traffic.
[0064] Control signals from OFDMA MAC 714 and downlink data streams
726 are mixed and modulated by OFDM modulator 716 for downlink
transmission. Subchannel formation (such as the antenna
beamforming/switching operations described below with reference to
FIG. 8) is performed by subchannel formation block 720 using
subchannel definition information stored in the subscribers'
channel profile register 608. The output of subchannel formation
block 720 is up-converted by the set of up-converters 722, and
transmitted through transmission antenna array 724.
[0065] Beacon signal generator 717 is used to generate a beacon
signal appropriate to the underlying transmission scheme. For
example, for an OFDMA transmission scheme, beacon signal generator
717 generates a signal including OFDMA pilot symbols interspersed
among test data frames.
[0066] Details of functional blocks corresponding to one embodiment
of an OFDMA transmitter module 800 for a base station having N
antennas are shown in FIG. 5. A MAC dynamic channel allocation
block 802 is used to select an appropriate antenna resource and
subchannel for each of P users, as depicted by selection inputs to
modem and subchannel allocation blocks 804.sub.1-P. Based on the
modem and subchannel allocation for each user, a corresponding
OFDMA baseband signal is generated, up-converted, and transmitted
over an appropriate antenna using signal-processing techniques that
are well-known in the OFDMA transmission arts. The process is
depicted by Fast Fourier Transform (FFT) blocks 804.sub.1-N,
parallel to serial (P/S) conversion blocks 806.sub.1-N, and add
cyclic prefix (CP) blocks 804.sub.1-N,
[0067] OFDMA transmitter module 800 performs antenna switching
operations by adjusting the FFT inputs. For example, for a given
subscriber channel, certain FFT inputs are set to 1 (meaning use),
while other FFT inputs are set to 0 (meaning ignore). OFDMA
transmitter module 800 also support channels that are facilitated
by concurrently sending signals over multiple antennas.
[0068] In general, the operations performed by the process and
functional blocks illustrated in the figures herein and described
above are performed by processing logic that may comprise hardware
(circuitry, dedicated logic, etc.), software (such as is run on a
general purpose computer system or a dedicated machine), or a
combination of both.
[0069] Whereas many alterations and modifications of the present
invention will no doubt become apparent to a person of ordinary
skill in the art after having read the foregoing description, it is
to be understood that any particular embodiment shown and described
by way of illustration is in no way intended to be considered
limiting. Therefore, references to details of various embodiments
are not intended to limit the scope of the claims which in
themselves recite only those features regarded as essential to the
invention.
* * * * *