U.S. patent application number 09/859415 was filed with the patent office on 2001-09-27 for method of improving quality of radio connection.
This patent application is currently assigned to Nokia Telecommunications Oy. Invention is credited to Katz, Marcos.
Application Number | 20010024173 09/859415 |
Document ID | / |
Family ID | 26160465 |
Filed Date | 2001-09-27 |
United States Patent
Application |
20010024173 |
Kind Code |
A1 |
Katz, Marcos |
September 27, 2001 |
Method of improving quality of radio connection
Abstract
The invention relates to a method of improving the quality of a
radio connection (170) in a cellular radio network. Relevant for
the invention, the cellular radio network includes a base station
system (126) and a subscriber terminal (150). A bidirectional radio
connection (170) using a directional antenna beam (304) is provided
between the base station system (126) and the subscriber terminal
(150). In the method, in the base station system (126) an angle of
incidence (302) of the directional antenna beam (304) is formed on
the basis of a received radio signal (170A) transmitted by the
subscriber terminal (150). The base station system (126) transmits
a radio signal (170B) to the subscriber terminal (150) in the
direction of an angle of departure (308) formed on the basis of the
angle of incidence (302). In accordance with the invention, a ratio
is formed for the imbalance between the downlink and uplink
traffics. The processing of the directional antenna beam (304) of
the radio signal (170A, 170B) is controlled on the basis of the
formed ratio.
Inventors: |
Katz, Marcos; (Oulu,
FI) |
Correspondence
Address: |
Pillsbury Winthrop LLP
Intellectual Property Group
East Tower, Ninth Floor
1100 New York Avenue, N.W.
Washington
DC
20005-3918
US
|
Assignee: |
Nokia Telecommunications Oy
|
Family ID: |
26160465 |
Appl. No.: |
09/859415 |
Filed: |
May 18, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09859415 |
May 18, 2001 |
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09341095 |
Oct 19, 1999 |
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6229481 |
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09341095 |
Oct 19, 1999 |
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PCT/FI98/00855 |
Nov 4, 1998 |
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Current U.S.
Class: |
342/367 |
Current CPC
Class: |
H04W 16/28 20130101;
H04B 7/0617 20130101 |
Class at
Publication: |
342/367 |
International
Class: |
H04B 007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 5, 1997 |
FI |
974149 |
Mar 19, 1998 |
FI |
980616 |
Claims
1. A method of improving the quality of a radio connection in a
cellular radio network including a base station system, a
subscriber terminal, and a bi-directional radio connection between
the base station system and the subscriber terminal using a
directional antenna beam the method comprising: forming an angle of
incidence of the directional antenna beam based on a received
uplink radio signal transmitted by the subscriber terminal;
transmitting, on a downlink, a radio signal to the subscriber
terminal in the direction of an angle of departure formed on the
basis of the angle of incidence; forming a ratio for imbalance
between downlink traffic and uplink traffic; and controlling
processing of the directional antenna beam on the basis of the
ratio.
2. The method of claim 1, wherein in the transmission on the
downlink comprises forming of the directional antenna beam is
controlled on the basis of the ratio.
3. The method of claim 1, further comprising controlling processing
of the directional antenna beam of the radio signal received by the
base station system from the subscriber terminal on the basis of
the ratio.
4. The method of claim 1, wherein the ratio is formed by
subtracting a number of signal received on the uplink during a
period of time from a number of signals transmitted on the downlink
during that given period of time; and dividing a difference thus
obtained by a sum of the number of signals transmitted on the
downlink and the number of signals received on the uplink, the sum
being formed using the same parameters that were used for forming
the difference.
5. The method of claim 4, wherein when the ratio obtains a value of
about zero, the traffics are deemed balanced.
6. The method of claim 4, wherein when the ratio obtains a value
greater than zero, the traffics are deemed unbalanced in such a
manner that the downlink traffic is heavier than the uplink
traffic.
7. The method of claim 4, wherein when the ratio obtains a value
lower than zero, the traffics are deemed unbalanced in such a
manner that the uplink traffic is heavier than the downlink
traffic.
8. The method of claim 4, wherein when the ratio obtains a value 1,
only the downlink has traffic.
9. The method of claim 4, wherein when the ratio obtains a value
-1, only the uplink has traffic.
10. The method of claim 1, further comprising selecting a suitable
algorithm for forming the directional antenna beam on the basis of
the ratio.
11. The method of claim 1, wherein a width of the directional
antenna beam is determined on the basis of the ratio.
12. The method of claim 11, wherein the width of the directional
antenna beam depends on an equation in which a proportionality
constant is divided by a difference, which difference is formed by
subtracting the ratio from a sensitivity parameter which is greater
than one.
13. The method of claim 11, wherein the width of the directional
antenna beam of the radio signal used by the base station system in
a radio connection directly depends on an uncertainty time elapsed
between formation of a last angle of incidence and use of the radio
signal.
14. The method of claim 13, wherein the width of the directional
antenna beam of the radio signal transmitted by the base station
system to the subscriber terminal directly depends on the
uncertainty time elapsed between the formation of the last angle of
incidence and a transmission moment.
15. The method of claim 13, wherein the width of the directional
antenna beam of the radio signal received by the base station
system from the subscriber terminal directly depends on the
uncertainty time elapsed between the formation of the last angle of
incidence and a reception moment.
16. The method of claim 13, wherein the width of the directional
antenna beam is increased in a direction of movement of the
subscriber terminal.
17. The method of claim 13, wherein the width of the directional
antenna beam of the radio signal used by the base station system in
a radio connection directly depends on the channel of the radio
connection established on the basis of a preceding radio signal
received by the subscriber terminal.
18. The method of claim 13, wherein the width of the directional
antenna beam of the radio signal used by the base station system in
the radio connection directly depends on time elapsed between
channel estimation of the radio connection performed on the basis
of a preceding radio signal received or transmitted by the
subscriber terminal, and a use of the radio signal.
19. The method of claim 13, wherein the dependence on the
uncertainty time is linear or in accordance with any other
increasing function.
20. The method of claim 13, wherein the width of the directional
antenna beam is changed in predetermined steps.
21. The method of claim 13, wherein the width of the directional
antenna beam is changed steplessly.
22. The method of claim 13, wherein the width of the directional
antenna beam is inversely affected by a distance between the base
station system and the subscriber terminal.
23. The method of claim 13, wherein the method is used in radio
connections comprising at least one of sporadic and asymmetric
traffic.
24. The method of claim 23, wherein the method is used in
connection with packet transmission.
25. A cellular radio network comprising: a base station system; a
subscriber terminal; and a bi-directional radio connection between
the base station system and the subscriber terminal using a
directional antenna beam, wherein the base station system is
configured to form an angle of incidence of the directional antenna
beam on the basis of a received uplink radio signal transmitted by
the subscriber terminal, and the base station system is configured
to transmit, on a downlink, a radio signal, to the subscriber
terminal in direction of an angle of departure formed on the basis
of the angle of incidence, and wherein the base station system is
configured to form a ratio for an imbalance between the downlink
traffic and the uplink traffic, control processing of the antenna
beam of the transmitted or received radio signal on the basis of
the ratio.
26. The cellular radio network of claim 25, wherein the base
station system is configured to form, on the basis of the ratio,
the directional antenna beam of the radio signal to be transmitted
to the subscriber terminal.
27. The cellular radio network of claim 25, wherein the base
station system is configured to form, on the basis of the ratio,
the directional antenna beam of the radio signal received from the
subscriber terminal.
28. The cellular radio network of claim 25, wherein the base
station system is configured to form the ratio by subtracting a
number of signals received on the uplink during a given period of
time from a number of the signals transmitted on the downlink
during that given period of time; and dividing the difference thus
obtained by a sum of the number of signals transmitted on the
downlink and the number of signals received on the uplink, the sum
being formed using the same parameters that were used for forming
the difference.
29. The cellular radio network of claim 28, wherein when the ratio
obtains a value of about zero, the traffics are deemed
balanced.
30. The cellular radio network of claim 28, wherein when the ratio
obtains a value greater than zero, the traffics are deemed
unbalanced in such a manner that the downlink traffic is heavier
than the uplink traffic.
31. The cellular radio network of claim 28, wherein when the ratio
obtains a value lower than zero, the traffics are deemed unbalanced
in such a manner that the uplink traffic is heavier than the
downlink traffic.
32. The cellular radio network of claim 28, wherein when the ratio
obtains a value 1, only the downlink has traffic.
33. The cellular radio network of claim 28, wherein when the ratio
obtains a value -1, only the uplink has traffic.
34. The cellular radio network of claim 25, wherein the base
station system is configured to select a suitable algorithm for
forming the directional antenna beam on the basis of the ratio.
35. The cellular radio network of claim 25, wherein the base
station system is configured to determine a width of the
directional antenna beam on the basis of the ratio.
36. The cellular radio network of claim 35, wherein the base
station system is configured in such a manner that the width of the
directional antenna beam depends on an equation in which a
proportionality constant is divided by a difference, which
difference is formed by subtracting the ratio from a sensitivity
parameter which is greater than one.
37. The cellular radio network of claim 35, wherein the base
station system is configured to form the width of the directional
antenna beam of a radio signal used in a radio connection to be
directly dependent on an uncertainty time elapsed between a
formation of a last angle of incidence and a use of the radio
signal.
38. The cellular radio network of claim 37, wherein the base
station system is configured to form the width of the directional
antenna beam of a radio signal to be transmitted to the subscriber
terminal to be directly dependent on the uncertainty time elapsed
between the formation of the last angle of incidence and a
transmission moment.
39. The cellular radio network of claim 37, wherein the base
station system is configured to form the width of the directional
antenna beam of a radio signal received from the subscriber
terminal to be directly dependent on the uncertainty time elapsed
between the formation of the last angle of incidence and a
reception moment.
40. The cellular radio network of claim 37, wherein the base
station system is configured to increase the width of the
directional antenna beam in a direction of movement of the
subscriber terminal.
41. The cellular radio network of claim 37, wherein the base
station system is configured to form the width of the directional
antenna beam of the radio signal used by the base station system in
the radio connection to be directly dependent on a channel of the
radio connection established on the basis of a preceding radio
signal received or transmitted by the subscriber terminal.
42. The cellular radio network of claim 37, wherein the base
station system is configured to form the width of the directional
antenna beam of the radio signal used by the base station system in
the radio connection to be directly dependent on the time elapsed
between a channel estimation of the radio connection performed on
the basis of the preceding radio signal received or transmitted by
the subscriber terminal, and a use of the radio signal.
43. The cellular radio network of claim 37, wherein the dependence
on the uncertainty time is linear or in accordance with any other
increasing function.
44. The cellular radio network of claim 37, wherein the width of
the antenna beam is changed in predetermined steps.
45. The cellular radio network of claim 37, wherein the width of
the directional antenna beam is changed steplessly.
46. The cellular radio network of claim 37, wherein the width of
the directional antenna beam is inversely affected by a distance
between the base station system and the subscriber terminal.
47. The cellular radio network of claim 37, wherein the cellular
radio network is used in radio connections comprising at least one
of sporadic and asymmetric traffic.
48. The cellular radio network of claim 47, wherein the cellular
radio network is used in connection with packet transmission.
Description
[0001] This application is a Continuation Application of U.S.
application Ser. No. 09/341,095 filed Jul. 2, 1999, which is the
National Phase of International Application PCT/FI98/00855 filed
Nov. 4, 19998 which designated the U.S. and that International
Application was Published under PCT Article 21(2) in English.
FIELD OF THE INVENTION
[0002] The invention relates to a method of improving the quality
of a radio connection in a cellular radio network, comprising a
base station system, a subscriber terminal and a bidirectional
radio connection between the base station system and the subscriber
terminal using a directional antenna beam; in which method in the
base station system, an angle of incidence of the directional
antenna beam is formed on the basis of a received uplink radio
signal transmitted by the subscriber terminal, and the base station
system transmits a radio signal on the downlink to the subscriber
terminal in the direction of an angle of departure formed on the
basis of the angle of incidence.
BACKGROUND OF THE INVENTION
[0003] A problem presented by the arrangement described above is
that it functions most properly when the radio connection between
the base station system and the subscriber terminal is balanced, in
other words radio signals travel regularly and symmetrically in
both directions. The problem in radio connections comprising
sporadic and/or asymmetrical traffic is that, because a long time
may have elapsed since the reception of a previous signal from the
subscriber terminal, the angle of departure does not necessarily
correspond to the actual location of the subscriber terminal.
During this time, the subscriber terminal may have moved too much
for the signal transmitted using the angle of departure formed on
the basis of the old angle of incidence to reach the subscriber
terminal. The properties of the channel used in the radio
connection also change on account of the change in the location. A
next signal received by using an out-of-date angle of incidence and
transmitted by the subscriber terminal can also be lost.
[0004] The problem is serious particularly in cellular radio
networks using packet transmission; in a typical packet
transmission, one party, for example the base station system,
transmits much data, and the subscriber terminal possibly only
transmits occasional retransmission requests. The use of a WWW
(World Wide Web) browser, for example, results in heavy traffic on
the downlink and light traffic on the uplink.
BRIEF DESCRIPTION OF THE INVENTION
[0005] An object of the invention is thus to provide a method and
equipment implementing the method so as to solve the above
problems. This can be achieved by a method described in the
introduction, which is characterized by forming a ratio for the
imbalance between the downlink traffic and the uplink traffic;
controlling the processing of the directional antenna beam of the
radio signal on the basis of the ratio.
[0006] The invention further relates to a cellular radio network
comprising a base station system, a subscriber terminal, and a
bidirectional radio connection between the base station system and
the subscriber terminal and using a directional antenna beam; and
on the uplink, the base station system forms an angle of incidence
of the directional antenna beam on the basis of a received radio
signal transmitted by the subscriber terminal, and on the downlink,
the base station system transmits a radio signal to the subscriber
terminal in the direction of an angle of departure formed on the
basis of the angle of incidence.
[0007] The cellular radio network of the invention is characterized
in that the base station system is arranged to form a ratio for the
imbalance between the downlink traffic and the uplink traffic,
control the processing of the antenna beam of the radio signal on
the basis of the ratio.
[0008] The preferred embodiments of the invention are disclosed in
the dependent claims.
[0009] The invention is based on the idea that in the base station
system, a ratio is formed between the amount of the traffic
transmitted on the downlink and the amount of the traffic received
on the uplink. By means of the ratio, problems occurring on the
radio path can easily be predicted and avoided.
[0010] Several advantages can be achieved by the method and
arrangement of the invention. The method enables directional
antenna beams to be used in radio connections comprising sporadic
and/or asymmetric traffic, particularly in packet radio systems.
The method enables the most suitable algorithm for processing the
directional radio beam to be selected for the situation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The invention is now described in closer detail in
connection with the preferred embodiments with reference to the
accompanying drawings, in which
[0012] FIG. 1 shows an example of a cellular radio network in
accordance with the invention,
[0013] FIG. 2 shows a transceiver,
[0014] FIGS. 3A, 3B show known antenna beams,
[0015] FIGS. 3C, 3D show antenna beams of the invention,
[0016] FIGS. 4A, 4B illustrate the conception of uncertainty
time,
[0017] FIG. 5 shows an example of how the ratio and the width of an
antenna beam depend on each other, and
[0018] FIG. 6 illustrates how the ratio is used for selecting an
algorithm for processing a directional radio beam.
DETAILED DESCRIPTION OF THE INVENTION
[0019] With reference to FIG. 1, a typical structure of a cellular
radio network in accordance with the invention is described. FIG. 1
only comprises matters that are relevant for describing the
invention, but it is obvious to those skilled in the art that a
common cellular radio network also comprises other functions and
structures, which need not to be described here in closer detail.
The invention is suitable for use in all kinds of cellular radio
networks in which above problems occur caused by radio connections
comprising sporadic and/or asymmetric traffic. The cellular radio
networks of the invention use SDMA (Space Division Multiple Access)
in the form of directional antenna beams. The antenna beams used
can most readily be formed by beamforming techniques.
[0020] The example shows the use of the invention in a cellular
radio network which uses TDMA (Time Division Multiple Access),
without being restricted thereto, however. The invention can thus
be used in cellular radio networks which use CDMA (Code Division
Multiple Access) and FDMA (Frequency Division Multiple Access), for
example, and in hybrid systems which use different multi-access
systems simultaneously.
[0021] A cellular radio network typically comprises a fixed network
infrastructure, in other words a network part, and subscriber
terminals 150, which can be fixedly located, situated in a vehicle
or portable terminals. The subscriber terminal 150 can be a common
GSM mobile telephone to which a portable computer 152, for example,
can be connected by an extension card, and which can be used in
packet transmission for ordering and processing packets. The
network part comprises base stations 100. A base station controller
102 connected to a plurality of base stations 100 controls them in
a centralized manner. A base station 100 comprises transceivers
114. The base station 100 typically comprises one to sixteen
transceivers 114. One transceiver 114 provides one TDMA frame, in
other words typically eight time slots, with radio capacity.
[0022] The base station 100 comprises a control unit 118, which
controls the operation of the transceivers 114 and a multiplexer
116. The traffic and control channels used by a plurality of
transceivers 114 are placed in one transmission connection 160 by
the multiplexer 116.
[0023] The transceivers 114 in the base station 100 are connected
to an antenna array 112 by which a bi-directional radio connection
170 is established to the subscriber terminal 150.
[0024] FIG. 2 shows in closer detail the structure of one
transceiver 114. The antenna array using directional antenna beams
comprises various separate elements 112A, 112B, such as eight
different elements, to direct an antenna beam in reception. The
number of the antenna elements 112A, 112B can be M, when M is any
integer greater than 1. The same antenna elements 112A, 112B can be
used in the transmission and in the reception, or alternatively,
the transmission can use unique antenna elements 112C, 112D, as
shown in FIG. 2. The arrangement of the antenna elements 112A,
112B, 112C, 112D can be linear or planar, for example.
[0025] Linearly, the elements can be arranged as ULA (Uniform
Linear Array), for example, in which the elements are placed in a
straight line at regular intervals. A planar arrangement, on the
other hand, can be a CA (Circular Array) in which the elements are
placed on the same plane horizontally in the form of the periphery
of a circle, for example. A certain part of the periphery of the
circle, for example 120 degrees, or even full 360 degrees, is then
covered. The one-level antenna structures mentioned above can, in
principle, also be implemented as two- or even three-dimensional
structures. A two dimensional structure is formed by placing ULA
structures in parallel, for example, whereby the elements form a
matrix.
[0026] A multipath-propagated signal is received via the antenna
elements 112A, 112B. Each antenna element 112A, 112B has a unique
receiver 200A, 200B, which are radio frequency parts 230.
[0027] A receiver 200 comprises a filter, which blocks frequencies
outside a desired frequency band. Next, the signal is converted
into intermediate frequency or directly into baseband, and in this
form the signal is sampled and quantized in an analogue/digital
converter 202A, 202B.
[0028] The multipath-propagated signals presented in a complex form
are next conveyed to a digital signal processing processor 232 with
its programs. The antenna pattern of the received signal is
directed by digital phasing of the signal, so the antenna elements
112A, 112B do not have to be mechanically steerable. Hence, the
direction of the subscriber terminal 150 is expressed as a complex
vector which is formed by elementary units corresponding to each
antenna element 112A, 112B and usually expressed as complex
numbers. Each separate signal is multiplied by the elementary unit
of the antenna element in weighting means 240. Next, the signals
can be combined in combining means 242.
[0029] Signal phasing can also be performed to a radio-frequency
signal or an intermediate-frequency signal possibly used. The
weighting means 240 are then located in connection with the radio
frequency parts 230 or between the radio frequency parts 230 and
the analogue/digital converters 202A, 202B.
[0030] Beamforming can also be performed analogically; the width of
the beams is then usually fixed. Using a Butler matrix, eight
different beams can be formed in the base station 100 sectored into
three sectors. If the width of each sector of the base station 100
is 120 degrees, so the width of a single beam is 15 degrees. The
width of the beam can thus be adjusted by using one or more beams,
whereby the width of the overall beam increases in steps of 15
degrees. In an extreme case, an omnidirectional antenna can be
achieved when all beams of all sectors are used for forming a
directional antenna beam. A base station system 126 can
simultaneously support different algorithms for forming the antenna
beam.
[0031] An equalizer 204 compensates for interference, such as
interference caused by multipath propagation. A demodulator 206
derives a bit stream which is conveyed to a demultiplexer 208 from
the equalized signal. The demultiplexer 208 separates the bit
stream from the different time slots into its unique, logical
channels. A channel codec 216 decodes the bit stream of the
different logical channels, in other words decides whether the bit
stream is signaling information, which is conveyed to a control
unit 214, or whether the bit stream is speech, which is conveyed to
a speech codec 122 of a base station controller 102. The channel
codec 216 also performs error correction. The control unit 214
performs internal control tasks by controlling the different
units.
[0032] In the transmission, a burst generator 228 adds a training
sequence and a tail to the data supplied from the channel codec
216. A multiplexer 226 assigns a unique time slot to each burst.
The signal is multiplied in weighting means 244 by an elementary
unit corresponding to each antenna element. In digital phasing, the
antenna beam can thus be directed in the direction of the complex
vector formed by the elementary units.
[0033] A modulator 224 modulates the digital signals into a
radiofrequency carrier wave. By using a digital/analogue converter
222A, 222B, the signal is converted from digital into analogue.
Each signal component is conveyed to a transmitter 220A, 220B
corresponding to each antenna element.
[0034] The transmitter 220A, 220B comprises a filter to restrict
the bandwidth. Furthermore, the transmitter 220A, 220B controls the
output capacity of the transmission. A synthesizer 212 arranges
necessary frequencies for the different units. The synthesizer 212
comprises a clock which can be controlled locally, or it can be
controlled in a centralized manner from somewhere else, for example
from the base station controller 102. The synthesizer 212 generates
the necessary frequencies by a voltage-controlled oscillator, for
example.
[0035] The base station controller 102 comprises a group switching
field 120 and a control unit 124. The group switching field 120 is
used for connecting speech and data, and for combining signaling
circuits. The base station system 126 formed by the base station
100 and the base station controller 102 further comprises the
transcoder 122. The transcoder is usually located as near to a
mobile switching centre 132 as possible since speech can then be
transmitted in the form of a cellular radio network between the
transcoder 122 and the base station controller 102 using as little
transmission power as possible.
[0036] The transcoder 122 converts the different digital forms of
speech coding used between a public switched telephone network and
the cellular radio network into compatible ones, for example from
the mode of 64 kbit/s of the fixed network to another mode (for
example of 13 kbit/s) of the cellular radio network, and vice
versa. The control unit 124 performs call control, mobility
management, collection of statistical information and
signaling.
[0037] As can be seen from FIG. 1, the group switching field 120
enables connections (depicted by the black dots) to a public
switched telephone network (PSTN) 134 to be established via the
mobile switching centre 132. In the public switched telephone
network, a typical terminal 136 is a common telephone or an
integrated services digital network (ISDN) telephone.
[0038] The invention is preferably implemented by software, whereby
the invention requires program modifications in a precisely defined
area in the control unit 118 of the base station 100 and/or in the
software of the digital signal processing processor of the
transceiver 114. The necessary modifications can thus be located
differently, depending on how the different programs with their
functions and responsibilities have been assigned between the
different parts of the base station system 126.
[0039] The bold line in FIG. 1 depicts how the data to be
transmitted travels from the subscriber terminal 150 in the
cellular radio network to a computer 148 connected to the public
switched telephone network. The data travels through the system on
an air interface 170, from the antenna 112 to a first transceiver
TRX1 114 and then, multiplexed in the multiplexer 116, over the
transmission connection 160 to the group switching field 120 in
which a connection is provided to the output of the transcoder 122,
and from the transcoder 122 the data is conveyed over the public
switched telephone network 134 to the computer 148. In the data
transmission, however, transcoding is not performed in the
transcoder 122, since this would change the contents of the data
transmitted.
[0040] FIG. 3A depicts how the signal is received from the
subscriber terminal 150. The base station system 126 knows in which
direction the subscriber terminal 150 is located (known as
Direction of Arrival). In the GSM system, for example, this
information is formed by utilizing the known training sequence
included in the received signal. Similarly, in the CDMA systems,
the location can be inferred on the basis of a received pilot
signal. Furthermore, "blind" estimating methods, which do not
require the received signal to include any known parts, can also be
used. The methods compute the direction from which the strongest
signal is received. The location of the subscriber terminal 150 can
also be found out in some other way. For the antenna array 112, the
direction is expressed as an angle 302 with respect to the
geographical west-east axis 300. The radio signal is received from
the subscriber terminal 150 via the antenna array 112 by using a
directional antenna beam 304.
[0041] FIG. 3B depicts how the subscriber terminal 150 has moved
during the packet transmission, but the base station system 126 has
not been informed of this. An angle of departure 308, which is used
in the transmission for directing the antenna beam 304 and formed
on the basis of the angle of incidence 302, is based on out-of-date
information about the location of the subscriber terminal 150.
Consequently, the antenna beam 304 is no longer directed towards
the subscriber terminal 150, and the quality of the connection
degrades; the connection may even be interrupted.
[0042] In the transmission, the base station system 126 can control
the following transmission parameters: the angle of departure 308
of the directional antenna beam 304, the width 306 of the
directional antenna beam 304, and the transmission power of the
radio signal. A suitable combination of these parameters yields an
optimum result.
[0043] Typically, when speech is transmitted, the amount of traffic
is almost identical on the downlink and the uplink, provided that
discontinuous transmission is not used.
[0044] When data is transmitted, the traffic is seldom balanced,
since the aim is usually to transmit information from one point to
another, for example transmission of data files, and searching
databases for information. Packet transmission is usually used for
real-time and non-real-time data transmission, although it can also
be used for real-time speech transmission.
[0045] When the traffic to be transmitted has grown heavier on the
downlink than on the uplink, the base station system 126 has fewer
opportunities to receive uplink radio signals, respectively. The
more irregularly bursts are received from the uplink, or the
smaller the amount of the bursts received from the uplink, which
contain the training sequence, the poorer the outcome of channel
estimation and the algorithm for forming the directional antenna
beam. Consequently, the downlink transmission parameters may not
meet the requirements set by the situation.
[0046] When the traffic is heavier on the uplink than on the
downlink, the accuracy of the channel estimates is good, and the
algorithm for forming the directional antenna beam is good both in
the transmission and reception.
[0047] In accordance with the invention, a ratio is formed for the
imbalance between the downlink traffic and the uplink traffic. The
ratio is then used for controlling the processing of the
directional antenna beam 304 of the radio signal.
[0048] The ratio is formed by the following formula: 1 ( T m ) = NB
D - NB U NB U + NB D ( 1 )
[0049] In the formula, the ratio .rho. indicates the imbalance
between the amount of traffic on the downlink and on the uplink
over a given period of time T.sub.m in the past. In the formula,
NB.sub.D represents the amount of traffic on the downlink, the
number of radio bursts, for example, and NB.sub.U represents the
amount of traffic on the uplink, respectively. Hence, in formula 1,
the ratio .rho. is obtained by subtracting from the number NB.sub.D
of the signals transmitted on the downlink during a given period of
time, the number NB.sub.U of the signals received on the uplink
during the same given period of time, and by dividing the
difference thus obtained by the sum of the number NB.sub.D of the
signals transmitted on the downlink and the number NB.sub.U of the
signals received on the uplink, said sum being formed using the
same parameters that were used for forming said difference.
[0050] The length of the time period T.sub.m depends on the
circumstances in the cellular radio network, mobility of the users,
and the distance between the base station 100 and the subscriber
terminal 150, etc. The length of the time period T.sub.m can be
controlled dynamically, for example, depending on the above
parameters. The time period T.sub.m can also be determined by
measurements, until a predetermined standard of quality is met.
[0051] By examining formula 1, it can be stated that when the ratio
.rho.(T.sub.m) obtains a value of about zero, the traffics are
balanced. When the ratio .rho.(T.sub.m) obtains a value greater
than zero, the traffics are unbalanced in such a manner that the
downlink traffic is heavier than the uplink traffic. When the ratio
.rho.(T.sub.m) obtains a value lower than zero, the traffics are
unbalanced in such a manner that the uplink traffic is heavier than
the downlink traffic. When the ratio .rho.(T.sub.m) obtains a value
1, only the downlink has traffic. When the ratio .rho.(T.sub.m)
obtains a value -1, only the uplink has traffic.
[0052] In the transmission, the forming of the directional antenna
beam 304 of the radio signal transmitted to the subscriber terminal
150 by the base station system 126 can be controlled on the basis
of the ratio .rho.(T.sub.m). Also in the reception, the processing
of the directional antenna beam 304 of the radio signal received by
the base station system 126 from the subscriber terminal 150 can be
controlled on the basis of the ratio. In the cellular radio
network, the invention can thus be utilized in both transmission
directions, or alternatively, only in one of them. The use of the
invention does not, of course, exclude the use of other methods,
but it can be used together with different methods using
directional antenna beams.
[0053] FIG. 6 illustrates how the choice of the algorithm for
processing the directional antenna beam is influenced by different
values of the ratio .rho.(T.sub.m). In the figure, the potential
values of the ratio .rho.(T.sub.m) from -1 to 1 are shown on the
x-axis. A curve FEASIBILITY depicts the feasibility of the
directional antenna beam for the circumstances. The greater the
value the curve FEASIBILITY obtains on the y-axis, the more
appropriate it is to use the directional antenna beam. A curve
DEGRADATION depicts how the performance of the directional antenna
beam degrades in the circumstances, respectively. The greater the
value the curve DEGRADATION obtains on the y-axis, the poorer the
performance of the directional antenna beam.
[0054] It was mentioned above that the controllable transmission
parameters include the transmission power, the angle of departure
308 of the directional antenna beam 304 and the width 306 of the
directional antenna beam 304. The angle of incidence of the
directional antenna beam 304 and the width 306 of the directional
antenna beam 304 can be controlled in the reception.
[0055] The width 306 of the directional antenna beam 304 either in
the transmission or in the reception can be determined on the basis
of the ratio .rho.(T.sub.m) by using the formula: 2 BW = G S - ( T
m ) ( 2 )
[0056] In formula 2, a parameter BW represents the width 306 of the
directional antenna beam 304, a parameter G is the proportionality
constant, S is a sensitivity parameter whose value varies depending
on the situation, always being greater than 1, however, and a
parameter .rho.(T.sub.m) is the ratio computed on the basis of
formula 1. The width BW of the antenna beam directed in accordance
with formula 2 depends on a formula in which the proportionality
constant G is divided by a difference which is formed by
subtracting the ratio .rho.(T.sub.m) from the sensitivity parameter
S which is greater than 1.
[0057] FIG. 5 illustrates how the width BW of the directional
antenna beam depends on the ratio .rho.(T.sub.m). The potential
values of the ratio .rho.(T.sub.m) from -1 to 1 are shown on the
x-axis, and the width BW of the directional antenna beam is shown
on the y-axis. The value of the proportionality constant G is set
to be 1, and the sensitivity parameter S is given three different
values 1.1 and 1.2 and 1.3 by turns. The continuous line represents
the curve corresponding to the sensitivity parameter value 1.1, the
broken line represents the curve corresponding to the value 1.2,
and the dotted line represents the curve corresponding to the value
1.3.
[0058] It can be seen from FIG. 5 that when the ratio
.rho.(T.sub.m) approaches the value 1, a wider directional antenna
beam BW is formed. When the ratio .rho.(T.sub.m) approaches a value
-1, a narrower directional antenna beam is formed, respectively.
When the traffic is balanced, the ratio .rho.(T.sub.m) obtains a
value zero, and the width of the directional antenna beam is
determined by the choice of the proportionality constant G, since
formula 2 then obtains the form BW=G/S.
[0059] The width of the directional antenna beam can be determined
by using formula 2 alone, or alternatively, formula 2 can be only
one of the control variables affecting the width of the directional
antenna beam. Using formula 2, the uncertainty of the uplink
estimation can, in principle, be compensated for by widening the
directional antenna beam used.
[0060] FIG. 5 illustrates how the sensitivity parameter S affects
the width BW of the directional antenna beam: the nearer the value
of the sensitivity parameter S is to 1, the more sensitive the
width of the directional antenna beam is to change when traffic
imbalance increases. It can also be seen from FIG. 5 that within
the value range from -1 to zero of the proportionality constant
.rho.(T.sub.m), in other words when the traffic is heavier on the
uplink, the width of the directional antenna beam is almost
identical, in other words it is extremely narrow. This is due to
the fact that the base station system 126 receives a sufficient
amount of information from the subscriber terminal 150, and thus
can reliably utilize the algorithms for forming the directional
antenna beam. The simplest way to choose the algorithm for forming
the directional antenna beam is to use a narrow directional antenna
beam within the value range from -1 to zero of the ratio
.rho.(T.sub.m), to start increasing the width of the directional
antenna beam within the value range above zero, and to stop using
the directional antenna beam, and possibly even use an
omnidirectional antenna, when approaching a value 1.
[0061] Instead of for controlling the width of the directional
antenna beam, formula 2 can also be used for indicating a
degradation of performance of the directional antenna beam, which
is caused by insufficient traffic on the uplink, as was shown in
connection with FIG. 6. This value can be observed in FIG. 5 by
replacing the control BW of the width of the antenna beam on the
y-axis by a parameter called "degradation of performance of the
directional antenna beam".
[0062] FIG. 3C illustrates the operation of the invention. The
subscriber terminal has moved from the situation of FIG. 3A as
described in FIG. 3B. The directional antenna beam 304 of the
invention has now been widened since the ratio .rho.(T.sub.m) has
become greater than zero.
[0063] According to a preferred embodiment of the invention, the
width 306 of the directional antenna beam 304 of the radio signal
used by the base station system 126 in the radio connection 170
further directly depends on the uncertainty time elapsed between
the formation of a last angle of incidence and the use of the radio
signal because such a long time has elapsed since the location of
the subscriber terminal 150 was last estimated that the subscriber
terminal 150 has probably moved. For example, by comparing FIGS. 3A
and 3C it can be seen that the width 306 of the directional antenna
beam 304 has increased to cover the assumed movement of the
subscriber terminal 150 in FIG. 3C and the quality of the
connection does not degrade.
[0064] The example of FIGS. 3A, 3C also applies to the received
signal in the base station system 126. The antenna pattern of the
signal received by the antenna array 112 can be directed in the
assumed direction of the subscriber terminal 150. The antenna beam
304 is widened in the reception to enable also the strongest
signals to be received. The width of the beam 304 can slightly (by
some degrees) be affected by changing the values of the elementary
units of the directional vector, but most efficiently it can be
affected by adjusting the number of the antenna elements 112A, 112B
used. The fewer elements 112A, 112B are used, the wider the beam
304 is. The more elements 112A, 112B are used, the narrower the
beam 304 can be, respectively. When analogue beamforming techniques
are used, the adjustment of the width of the beam 304 is quantized,
whereby it can be adjusted step by step, in steps of fifteen
degrees, for example, by increasing or decreasing the number of the
partial beams of the beam 304.
[0065] FIG. 4A illustrates the concept of uncertainty time. A radio
signal 170A transmitted by the subscriber terminal 150 has been
received at a point of time t1 in the base station system 126. At a
point of time t2, the angle of incidence 302 indicating the
direction towards the subscriber terminal 150 is formed on the
basis of the received radio signal 170A. At a point of time t3, the
base station system 126 transmits a radio signal 170B in the
direction of the angle of departure 308 formed on the basis of the
angle of incidence 302. An uncertainty time 400A is now the time
that has elapsed between the point of time when the direction of
the subscriber terminal 150 was last estimated and the point of
time when the signal is transmitted in the estimated direction of
the subscriber terminal 150. The longer the uncertainty time 400A
becomes, the more improbable it is that the subscriber terminal 150
is located in the original direction.
[0066] Similarly, FIG. 4B illustrates the uncertainty time with
respect to the reception. Again, the radio signal 170A transmitted
by the subscriber terminal 150 has been received at the point of
time t1. At the point of time t2, the angle of incidence 302
indicating the direction towards the subscriber terminal 150 is
formed on the basis of the received radio signal 170A. At the point
of time t3, the base station system 126 receives a next signal 170A
transmitted by the subscriber terminal 150 using as the direction
of the antenna beam 304 the angle of incidence 302 estimated at the
point of time t2. An uncertainty time 400B is now the time that has
elapsed between the point of time when the direction of the
subscriber terminal 150 was last estimated and the point of time
when the signal is received from the estimated direction of the
subscriber terminal 150. The longer the uncertainty time 400B
becomes, the more improbable it is that the subscriber terminal 150
is located in the original direction.
[0067] In the base station system 126, the width 306 of the antenna
beam 304 is thus increased according to the uncertainty time in the
transmission and/or the reception. The dependence can be linear or
in accordance with any other increasing function. The width 306 of
the antenna beam 304 can be changed steplessly or in predetermined
steps.
[0068] FIG. 3D shows a preferred embodiment in which the width 306
of the antenna beam 304 is increased only in the direction of the
assumed movement of the subscriber terminal 150. The direction of
the movement can be estimated on the basis of the previous
locations of the subscriber terminal 150. This has the advantage
that the antenna beam 304 is not unnecessarily widened.
[0069] The width 306 of the antenna beam 304 preferably described
is, in addition to the uncertainty time, also affected by the
distance between the base station system 126, more specifically its
antenna array 112, and the subscriber terminal 150. When this
distance is short, and when the subscriber terminal 150 moves even
for a relatively short period of time, a change of dozens of
degrees in its direction results, seen from the antenna array 112.
When the distance is long, the change of the angle is typically
only a few degrees, respectively. The dependence can be implemented
for example in such a manner that the width 306 of the antenna beam
304 increases when the uncertainty time increases, but how much it
increases depends on the distance between the base station system
126 and the subscriber terminal 150 in such a manner that when the
distance is short, the width increases greatly, and decreases when
the distance becomes longer.
[0070] In a preferred embodiment of the invention, in addition to
or instead of the uncertainty time described above, the width 306
of the directional antenna beam 304 is affected by the properties
of the channel of the radio connection 170. In the base station
system 126, the channel of the radio connection 170 is estimated by
utilizing the known part, the training sequence for example,
included in the signal. When the channel quality is poor, the
antenna beam 304 can be widened in order to improve the quality. A
linear relation, for example, can be defined between the quality
standards or other properties of the channel and the width of the
beam 304.
[0071] Although the subscriber terminal 150 does not move at all,
the channel may be changed in some circumstances. The quality of
the channel can then be restored to an adequately high level by
widening the beam 304. Let us assume a situation, for example, in
which the subscriber terminal 150 is placed in a car. The quality
of the radio connection 170 is extremely high since the subscriber
terminal has a direct visual connection to the antenna 112 of the
base station 100. A very narrow and precisely directed antenna beam
304 is then used. Next, a truck moves in front of the car, blocking
the direct visual connection to the antenna 112. Consequently, the
quality of the radio connection 170 degrades, which is detected in
the base station system 126 in connection with channel estimation.
By widening the directional antenna beam 304 the quality of the
radio connection 170 can be restored to the former level. This is
partly affected by the multipath propagation of the signal.
[0072] If a long time has elapsed since the channel estimation
performed on the basis of the received signal, the width 306 of the
antenna beam 304 can directly depend on the time elapsed between
the channel estimation of the radio connection 170 performed on the
basis of the previous received radio signal transmitted by the
subscriber terminal 150 and the use of the radio signal. In
principle, this corresponds to the main embodiment of the
invention, but instead of the formation of the angle of incidence,
the determining factor is now the length of the time elapsed since
channel estimation.
[0073] Although the invention is described above with reference to
the example in accordance with the accompanying drawings, it is
obvious that the invention is not restricted thereto but it can be
modified in many ways within the scope of the inventive idea
disclosed in the attached claims.
* * * * *