U.S. patent application number 10/360486 was filed with the patent office on 2004-09-09 for allocation of sub channels of mimo channels of a wireless network.
Invention is credited to Wilson, Fiona, Wilson, Keith S..
Application Number | 20040176097 10/360486 |
Document ID | / |
Family ID | 32926164 |
Filed Date | 2004-09-09 |
United States Patent
Application |
20040176097 |
Kind Code |
A1 |
Wilson, Fiona ; et
al. |
September 9, 2004 |
Allocation of sub channels of MIMO channels of a wireless
network
Abstract
A base station for a wireless network uses one or more MIMO
channels having subchannels, to communicate with multiple user
equipments, and allocates the sub channels to the user equipments.
Different subchannels of a given one of the channels can be
allocated to different user equipments. The ability to allocate sub
channels individually rather than only allocating entire channels
can enable higher data rates can be achieved. This is particularly
useful for improving data rates at cell boundaries or sector
boundaries, where the coverage is traditionally weakest. A user
equipment can use subchannels from different MIMO channels from
different sectors or from different base stations.
Inventors: |
Wilson, Fiona; (Spellbrook,
GB) ; Wilson, Keith S.; (Bishops Stortford,
GB) |
Correspondence
Address: |
William M. Lee, Jr.
Barnes & Thornburg
P.O. Box 2786
Chicago
IL
60690-2786
US
|
Family ID: |
32926164 |
Appl. No.: |
10/360486 |
Filed: |
February 6, 2003 |
Current U.S.
Class: |
455/452.2 ;
455/561 |
Current CPC
Class: |
H04L 5/006 20130101;
H04B 7/0632 20130101; H04L 5/0023 20130101; H04L 5/0037 20130101;
H04L 5/0035 20130101; H04W 72/044 20130101; H04W 36/18 20130101;
H04B 7/0413 20130101; H04W 88/08 20130101; H04W 72/1231 20130101;
H04B 7/0491 20130101; H04B 7/0417 20130101; H04B 7/022 20130101;
H04L 5/0085 20130101; H04L 5/0094 20130101; H04L 5/02 20130101 |
Class at
Publication: |
455/452.2 ;
455/561 |
International
Class: |
H04M 001/00 |
Claims
1. A base station for a wireless network for communicating over one
or more channels to multiple user equipments, at least one of the
channels having sub channels distinguishable by spatial separation
of transmitters of the respective sub channels, the base station
having an allocator for allocating the sub channels to the user
equipments, the allocator being arranged to allocate different
subchannels of a given one of the channels to different user
equipments.
2. The base station of claim 1, arranged to cooperate with a
neighboring base station to enable subchannels from both base
stations to be allocated to the same user equipment.
3. The base station of claim 1, the allocator being arranged to
allocate the sub channels for downlinks according to information
relating to sub channel signal quality received from the user
equipment.
4. The base station of claim 3, the information comprising signal
quality measurements of sub channels allocated to the user
equipment, and sub channels available but not allocated.
5. The base station of claim 3, the information comprising a
request to allocate a different sub channel.
6. The base station of claim 1, having different transmitters for
different sectors, the allocator being arranged to allocate sub
channels from more than one sector to the same user equipment.
7. The base station of claim 1, having a signal quality detector
for measuring signal quality of uplinks, the allocator using these
measurements to allocate sub channels for the uplink.
8. The base station of claim 1, arranged to adapt modulation and/or
coding of the sub channels.
9. A user equipment for communicating with a base station of a
wireless network over multiple channels, at least some of the
channels having sub channels distinguishable by spatial separation
of transmitters of the respective sub channels, the user equipment
having a signal quality detector for measuring the signal quality
of sub channels, and being arranged to use subchannels selected
from more than one of the channels.
10. The user equipment of claim 9 arranged to compare sub channels
from different base stations.
11. The user equipment of claim 9 arranged to compare sub channels
from different sectors of a base station.
12. The user equipment of claim 9 arranged to send signal quality
measurements of the sub channels to the base station.
13. An allocator for the base station of claim 1, in the form of
software.
14. A method of allocating sub channels in a wireless network
having multiple channels between a base station and multiple user
equipments, at least some of the channels having sub channels
distinguishable by spatial separation of transmitters of the
respective sub channels, the method having the steps of receiving
an indication of signal qualities of the sub channels, and
allocating the different subchannels of a given one of the channels
to different user equipments according to the signal qualities.
15. A method of offering a data transmission service over a
wireless network using the base station of claim 1.
16. A base station for a wireless network for communicating over
one or more channels to multiple user equipments, at least one of
the channels having sub channels distinguishable by spatial
separation of transmitters of the respective sub channels, the base
station having an allocator for allocating more than one of the
channels to a given one of the user equipments.
17. The base station of claim 16, further arranged to cooperate
with other base stations to allocate channels from more than one
base station to the given user equipment.
18. A user equipment for communicating with a base station of a
wireless network over multiple channels, at least some of the
channels having sub channels distinguishable by spatial separation
of transmitters of the respective sub channels, the user equipment
having a signal quality detector for measuring the signal quality
of sub channels, and being arranged to use more than one of the
channels simultaneously.
Description
FIELD OF THE INVENTION
[0001] This invention relates to base stations for wireless
networks, to user equipments for wireless networks, to methods of
allocating sub channels and to methods of offering a data
transmission service over such networks.
BACKGROUND TO THE INVENTION
[0002] A MIMO (Multiple Input, multiple output) wireless
communication system (see FIG. 1) is one which comprises a
plurality of antennas at the transmitter and one or more antennas
at the receiver. The antennas are employed in a multi-path rich
environment such that due to the presence of various scattering
objects (buildings, cars, hills, etc.) in the environment, each
signal experiences multipath propagation. Thus there are numerous
scattered signals between the transmit and receive antennas. User
data is transmitted from the transmit antennas using a MIMO
transmission method for example space-time coding (STC) or BLAST as
is known in the art, typically with many channels separated by
frequency, time slots, or coding. The receive antennas capture the
transmitted signals and a signal processing technique is then
applied as known in the art, to separate the transmitted signals
and recover the user data.
[0003] FIG. 1 shows a base station BS1 having two or more spatially
separated antennas, transmitting to corresponding antennas on user
equipment UE1. It is not untypical for one of the MIMO channels to
have much better reception than the other, despite the close
proximity of the respective antennas.
[0004] MIMO wireless communication systems are advantageous in that
they enable the capacity of the wireless link between the
transmitter and receiver to be improved compared with previous
systems in the respect that higher data rates can be obtained. The
multipath rich environment enables multiple channels (these are
what are referred to as sub-channels in the remainder of the
document) to be transmitted between the transmitter and receiver,
and distinguished at the receiver only by the spatial
characteristics, even though the same frequency, code or time slot
is used. Even line of sight signals can potentially be separated
into MIMO sub channels based on spatial characteristics. Data for a
single user can then be transmitted over several paths in the air
by inverse multiplexing the data into several streams. These are
transmitted simultaneously using the same frequency or time slots
or codes, and remultiplexed at the receiver. Consequently, higher
spectral efficiencies are achieved than with non-MIMO systems.
[0005] Also, as the multipath characteristic varies with time,
especially for mobile users, adaptive modulation coding (AMC) can
be used to achieve higher data rates where the multipath and
interference and noise allow. Conventional hand off techniques are
used in cell based MIMO systems to hand off all streams of a MIMO
channel to a neighboring base station. The trigger for such a
"hard" hand off is usually a signal strength indication of the
downlink, measured at the user equipment.
[0006] US Patent Application 20030003863 shows link adaptation for
MIMO transmission schemes. Information to be transmitted is divided
into a plurality of subsignals (defined as the signal carried on a
subchannel). In the receiver the different receive signals are
processed so that subsignals are detected and decoded and the
contribution of each detected and decoded subsignal is subtracted
from the receive signals. A feedback channel from receiver to
transmitter is used to send control information to the transmitter
to optimize the usage of the MIMO channel. In the receiver, the
link quality of each subsignal is determined and is transmitted to
the receiver via the feedback channel. In the transmitter, the link
quality information can be used to vary the data rate of each
subsignal, vary the transmit power of each subsignal, vary the
modulation scheme of each subsignal, vary the coding scheme of each
subsignal or vary any combination of these properties. Furthermore,
the link quality determination may be based on an error rate
measurement, a noise ratio measurement, or a capacity measurement
The link quality measurement may be fast-adaptive, e.g. when it is
based on the instantaneous calculated capacities of each subsignal.
Fast means that the measurement period is shorter or substantially
equal to the time period in which fast fading becomes relevant. As
fast fading is dependant on the Doppler shift of the signal, the
time period is also dependent on the velocity a receiver moves
relative to the transmitter. For slow-adaptive embodiments a
capacity calculation based on an average of the calculated
capacities of each layer with respect to a longer time period or a
capacity calculation that takes the outage of the calculated
capacities of each layer with respect to a longer time period, may
be applied.
[0007] One limitation with existing MIMO systems concerns the large
size of the transmit and receive antenna arrays. Another limitation
with existing MIMO systems is that they are designed for use in
environments where scattering occurs rather than for line of sight
situations. More significant in many cases are the following
limitations:
[0008] a) The coverage of MIMO systems can be very uneven. MIMO
provides much improved data rates for users with good C/I,
typically near the base station, but provides little improvement to
users in a poor C/I situation (typically at cell edges) so their
data rate remains low.
[0009] b) The `sub-channels` of a MIMO system often have very
uneven capacity. This is dependent on the propagation
characteristics of the channel and can be particularly uneven in a
propagation environment where one multipath component is very
dominant. These poor quality sub-channels are used to provide a
very small additional data rate to the user which is wasteful.
SUMMARY OF THE INVENTION
[0010] It is an object of the present invention to provide improved
apparatus and methods. According to a first aspect of the present
invention, there is provided a base station for a wireless network
for communicating over one or more channels to multiple user
equipments, at least one of the channels having sub channels
distinguishable by spatial separation of transmitters of the
respective sub channels, the base station having an allocator for
allocating the sub channels to the user equipments, the allocator
being arranged to allocate different subchannels of a given one of
the channels to different user equipments.
[0011] Notably, the ability to allocate sub channels individually,
rather than only allocating entire channels can enable higher data
rates to be achieved. It is based on a recognition that different
sub channels can support widely differing data rates to a given
user equipment, so it might be more efficient to reallocate a sub
channel having a lower data rate to a different user equipment for
which it can achieve a higher data rate. This is particularly
useful for improving data rates at cell boundaries or sector
boundaries, where the coverage is traditionally weakest. The
channels can be MIMO, for use with MIMO capable user equipment or
MISO (Multiple input single Output) with appropriate signal
processing at the receiver.
[0012] In principle, an alternative is to make the allocation at
the user equipment. It is usually more convenient to make the
allocation at the transmitter side, which is the base station for
the downlink. This is preferred because the base station has
information on the signal quality and data rate requirements of all
users so can allocate MIMO subchannels based on upon that more
complete knowledge of the network. The allocation for the uplink
can follow the downlink allocation or be allocated independently.
The latter is preferred if the fading characteristics of the
propagation channel has low correlation between the uplink and
downlink. If there is good correlation between uplink and downlink
fading, then using the downlink allocation will be a good
approximation.
[0013] The base station can be of any type. It need not necessarily
be at a fixed location, and can be distributed or incorporated
partly into mobile terminals in principle, without losing the
advantages set out above.
[0014] An additional feature of some embodiments is the base
station being arranged to cooperate with a neighboring base station
to enable subchannels from both base stations to be allocated to
the same user equipment.
[0015] This is particularly useful for user equipment near the
boundary of coverage from two base stations.
[0016] An additional feature of some embodiments is the allocator
being arranged to allocate the sub channels for downlinks according
to information relating to sub channel signal quality received from
the user equipment. This can help ensure the allocation is made
with the best information available.
[0017] An additional feature of some embodiments is the information
comprising signal quality measurements of sub channels allocated to
the user equipment, and sub channels available but not allocated.
This is the "raw" information useful for optimizing the
allocation.
[0018] An additional feature of some embodiments is the information
comprising a request to allocate a different sub channel. This is
intended to cover the option of the "raw" information being
processed in the user equipment so that less information need be
passed to the base station.
[0019] An additional feature of some embodiments is different
transmitters for different sectors, the allocator being arranged to
allocate sub channels from more than one sector to the same user
equipment. This is particularly useful for user equipment located
near the boundary of sectors.
[0020] An additional feature of some embodiments is a signal
quality detector for measuring signal quality of uplinks, the
allocator using these measurements to allocate sub channels for the
uplink. Independent allocation of uplinks can improve overall
efficiency.
[0021] An additional feature of some embodiments is the base
station being arranged to adapt modulation and/or coding of the sub
channels. This can further help improve coverage at the highest
data rates. The adaptation can be on the basis of measurements of
signal quality.
[0022] The invention also provides a user equipment for
communicating with a base station of a wireless network over
multiple channels, at least some of the channels having sub
channels distinguishable by spatial separation of transmitters of
the respective sub channels, the user equipment having a signal
quality detector for measuring the signal quality of sub channels,
and being arranged to use subchannels selected from more than one
of the channels.
[0023] This is notable for enabling more efficient use of potential
available capacity.
[0024] An additional feature of some embodiments is comparing sub
channels from different base stations.
[0025] An additional feature of some embodiments is comparing sub
channels from different sectors of a base station.
[0026] An additional feature of some embodiments is sending signal
quality measurements of the sub channels to the base station.
[0027] The invention also provides an allocator for the base
station, in the form of software. This acknowledges that software
can be a valuable, separately tradable commodity. It is intended to
encompass software, which runs on or controls "dumb" or standard
hardware, to carry out the desired functions. For similar reasons,
it is also intended to encompass software which "describes" or
defines the configuration of hardware, such as HDL (hardware
description language) software, as is used for designing silicon
chips, or for configuring universal programmable chips, to carry
out desired functions.
[0028] The invention also provides a method of allocating sub
channels in a wireless network having multiple channels between a
base station and multiple user equipments, at least some of the
channels having sub channels distinguishable by spatial separation
of transmitters of the respective sub channels, the method having
the steps of receiving an indication of signal qualities of the sub
channels, and allocating the different subchannels of a given one
of the channels to different user equipments according to the
signal qualities.
[0029] The invention also provides a method of offering a data
transmission service over a wireless network using the base station
The advantages of the invention can enable improvements to be made
in the system or network performance such as being more reliable
(better coverage of higher data rates for example) or more
flexible, having a greater capacity, or being more cost effective.
Consequently data transmission services over the network can be
enhanced, and the value of such services can increase Such
increased value of services over the life of the system, could
prove far greater than the sales value of the equipment.
[0030] Another aspect of the invention provides a base station for
a wireless network for communicating over one or more channels to
multiple user equipments, at least one of the channels having sub
channels distinguishable by spatial separation of transmitters of
the respective sub channels, the base station having an allocator
for allocating more than one of the channels to a given one of the
user equipments.
[0031] This can include all the subchannels, or involve selecting
the best subchannels from each channel.
[0032] An additional feature of some embodiments is the base
station being arranged to cooperate with other base stations to
allocate channels from more than one base station to the given user
equipment.
[0033] The invention also provides user equipment for communicating
with a base station of a wireless network over multiple channels,
at least some of the channels having sub channels distinguishable
by spatial separation of transmitters of the respective sub
channels, the user equipment having a signal quality detector for
measuring the signal quality of sub channels, and being arranged to
use more than one of the channels simultaneously.
[0034] Any of the features can be combined with any of the aspects
of the invention as would be apparent to those skilled in the art.
Other advantages will be apparent to those skilled in the art.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] To show by way of example how the invention can be
implemented, embodiments will now be described with reference to
the figures in which.
[0036] FIG. 1 shows a base station and user equipment of a prior
art MIMO arrangement,
[0037] FIGS. 2 and 3 show schematic views of embodiments of the
invention using two base stations and user equipment
[0038] FIG. 4 shows a sequence chart of the arrangement of FIG.
2,
[0039] FIG. 5 shows a schematic view of an embodiment using
multiple MIMO channels from a single base station, and
[0040] FIG. 6 shows a sequence chart of the arrangement of FIG.
5
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0041] FIGS. 2 and 3. Embodiment Using Two Base Stations
[0042] FIG. 2 shows base station BS1 in cell 1 and base station BS2
in cell 2. User equipment UE1 is initially served by a MIMO channel
from BS1 having subchannels 1 and 2. As UE1 moves towards BS2 it is
additionally served by a MIMO channel from BS2, without dropping
the MIMO channel from BS1. This means that data rate coverage in
cell border regions can be improved, since UE1 has four subchannels
to receive data. To achieve this, the traffic for UE1 needs to be
split by an RNC (radio network controller) between BS1 and BS2.
This can he implemented by signalling over management channels to
advise the RNC which base stations can serve UE1, following
conventional practice.
[0043] FIG. 3 shows another embodiment using two base stations.
Similar elements are shown to those in FIG. 2 and corresponding
reference signs are used where appropriate. In FIG. 3 two user
equipments UE1 and UE2 are in a cell border region. UE1 is
initially served by a MIMO channel from BS1. UE2 is initially
served by a MIMO channel from BS2. Both MIMO channels have two
subchannels. For each MIMO channel one of the subchannels is
stronger than the other. If UE1 detects a stronger signal from BS2
than the poorer of its subchannels from BS1, it will request that
it receives that stronger subchannel from BS2. Likewise if UE2
detects a stronger signal from BS1 it will request that it receives
that stronger subchannel from BS1. As shown in the figure, UE1 will
drop its poorer subchannel from BS1 and add a stronger subchannel
from BS2. UE1 will ignore the poorer subchannel from BS2. Likewise
UE2 will add the stronger subchannel from BS1 ignore the poorer
subchannel from BS1 and drop its poorer from BS2. The respective
subchannels which are dropped are taken up by the other user
equipment which can achieve a higher data rate since there is
better reception. Hence this swapping of subchannels can improve
the data rate for both user equipments, and overall network
capacity is improved in the cell border areas which are
conventionally the areas of worst coverage.
[0044] FIG. 4. Sequence Chart for FIG. 2
[0045] This chart shows some of the principal actions of each of
the entities. As a preliminary step BS1 and BS2 periodically report
to the RNC which base stations are nearest to a given UE. The RNC
then sends all the traffic for a given UE to several "best" base
stations UE1 regularly measures pilot signal quality. Pilot signals
are sent out by all base stations. If UE1 finds that the signal
from BS2 is stronger than any other the subchannels it is currently
using from BS1, it will report the measurements or request a change
of allocation. The base stations will determine a new allocation
according to the measurements for the requests. The new allocation
information will be sent to UE1 over a management channel then
transmissions can start to UE1 from both base stations.
[0046] FIG. 5, Embodiment Using Multiple MIMO Channels From a
Single Base Station
[0047] FIG. 5 shows an embodiment in which there are multiple MIMO
channels from a single base station. These channels can correspond
to different sectors of the base station, or the same sector. User
equipments UE1 and UE2 are served by base station BS1.
Conventionally and initially UE1 is served on MIMO Channel 1
(subchannels 1 and 2) and UE2 is served on Channel 2 (subchannels 1
and 2). If as shown subchannel 2 of channel 1 becomes poor in terms
of signal quality, it can be dropped. If subchannel 1 of channel 2
becomes poor it can be dropped. If the signal quality of these poor
channels is better at another UE, then a reallocation of sub
channels can take place. As shown, UE1 is now served on channel 1
subchannel 1 and channel 2 sub-channel 1. UE2 is now served on
channel 1 subchannel 2 and channel 2 sub-channel 2. Coverage can be
improved (UE1 and UE2 have improved their data rate). In addition
the network capacity can be improved. This represents a way of
optimising for network capacity while also improving coverage shown
operating in a single cell.
[0048] FIG. 6, Sequence Chart for the Embodiment of FIG. 5
[0049] FIG. 6 shows a sequence chart for the embodiment of FIG. 5.
As before, the user equipment measures pilot signal quality. UE1
and UE2 send measurement information or request service on the best
sub channels. BS1 then allocates the subchannels according to the
measurements or according to the requests. The allocation
information is sent to UE1 and UE2 over a management channel. Then
transmission of the traffic can begin.
[0050] Concluding Remarks
[0051] As has been described above, a base station for a wireless
network uses one or more MIMO channels having subchannels, to
communicate with multiple user equipments, and allocates the sub
channels to the user equipments. Different subchannels of a given
one of the channels can be allocated to different user equipments.
The ability to allocate sub channels individually, rather than only
allocating entire channels can enable higher data rates can be
achieved. This is particularly useful for improving data rates at
cell boundaries or sector boundaries, where the coverage is
traditionally weakest. A user equipment can use subchannels from
different MIMO channels from different sectors or from different
base stations.
[0052] Other variations will be apparent to those skilled in the
art, having corresponding advantages to those set out above, within
the scope of the claims.
* * * * *