U.S. patent application number 12/715665 was filed with the patent office on 2010-06-24 for method of using a: mobile unit to determine whether to commence handover.
This patent application is currently assigned to INTERDIGITAL TECHNOLOGY CORPORATION. Invention is credited to Stephen E. Terry, Ariela Zeira, Eldad Zeira.
Application Number | 20100157948 12/715665 |
Document ID | / |
Family ID | 26910687 |
Filed Date | 2010-06-24 |
United States Patent
Application |
20100157948 |
Kind Code |
A1 |
Zeira; Eldad ; et
al. |
June 24, 2010 |
METHOD OF USING A: MOBILE UNIT TO DETERMINE WHETHER TO COMMENCE
HANDOVER
Abstract
A method of using a mobile unit in a multi-cell communication
system to determine whether to commence handover of the mobile unit
from a serving base station located in a first cell of the
communication system to a target base station located in a second
cell of the communication system. The mobile unit determines the
serving base station received signal code power (RSCP.sub.ser), the
first cell interference signal code power (ISCP.sub.ser), the
target base station received signal code power (RSCP.sub.tar) and
the second cell interference signal code power (ISCP.sub.tar). If
the ratio RSCP.sub.ser/ISCP.sub.ser is less than the ratio
RSCP.sub.tar/ISCP.sub.tar, the mobile unit commences handover to
the target base station. The multi-cell communication system may be
a time division duplex (TDD) system. The mobile unit may send a
message to a radio network controller (RNC) in communication with
the serving and target base stations to initiate the handover.
Inventors: |
Zeira; Eldad; (Huntington,
NY) ; Zeira; Ariela; (Huntington, NY) ; Terry;
Stephen E.; (Northport, NY) |
Correspondence
Address: |
VOLPE AND KOENIG, P.C.;DEPT. ICC
UNITED PLAZA, SUITE 1600, 30 SOUTH 17TH STREET
PHILADELPHIA
PA
19103
US
|
Assignee: |
INTERDIGITAL TECHNOLOGY
CORPORATION
Wilmington
DE
|
Family ID: |
26910687 |
Appl. No.: |
12/715665 |
Filed: |
March 2, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10966449 |
Oct 15, 2004 |
7680080 |
|
|
12715665 |
|
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|
|
10216120 |
Aug 9, 2002 |
7068626 |
|
|
10966449 |
|
|
|
|
60312821 |
Aug 16, 2001 |
|
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Current U.S.
Class: |
370/332 |
Current CPC
Class: |
H04W 36/30 20130101 |
Class at
Publication: |
370/332 |
International
Class: |
H04W 36/00 20090101
H04W036/00 |
Claims
1. A method implemented in a user equipment (UE), the method
comprising: receiving a first signal and a second signal, wherein
the first signal is associated with a first base station and the
second signal is associated with a second base station; generating
channel quality indicator (CQI) based on the first signal and the
second signal, wherein the CQI includes signal strength information
and signal interference information; and transmitting the CQI to
initiate a handover from the first base station to the second base
station.
2. The method of claim 1, wherein the UE receives a physical
channel that carriers the first signal and receives another
physical channel that carriers the second signal.
3. The method of claim 1, further comprising measuring the signal
interference in at least one broadcast channel (BCH) timeslot.
4. The method of claim 1, wherein the signaling is performed via a
code division multiple access (CDMA) network.
5. A user equipment (UE) comprising: a receiver configured to
receive a first signal and a second signal, wherein the first
signal is associated with a first base station and the second
signal is associated with a second base station; a processor
configured to generate a channel quality indicator (CQI) based on
the first signal and the second signal, wherein the CQI includes
signal strength information and signal interference information;
and a transmitter configured to transmit the CQI to initiate a
handover from the first base station to the second base
station.
6. The method of claim 5, wherein the UE receives a physical
channel that carriers the first signal and receives another
physical channel that carriers the second signal.
7. The method of claim 5, further comprising measuring the signal
interference in at least one broadcast channel (BCH) timeslot.
8. The method of claim 5, wherein the signaling is performed via a
code division multiple access (CDMA) network.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 10/966,449, filed Oct. 15, 2004, which is a
continuation of U.S. patent application Ser. No. 10/216,120, filed
Aug. 9, 2002, now U.S. Pat. No. 7,068,626, issued Jun. 27, 2006,
which claims priority from U.S. Provisional Patent Application No.
60/312,821, filed Aug. 16, 2001, which are incorporated by
reference as if fully set forth.
BACKGROUND
[0002] The present invention generally relates to code division
multiple access (CDMA) communication systems employing time
division duplex (TDD). More specifically, the present invention is
a TDD system which implements a novel method for handing over a
mobile terminal between two base stations.
[0003] A Universal Mobile Telecommunications System (UMTS) network
architecture as shown in FIG. 1 includes a core network (CN), a
UMTS Terrestrial Radio Access Network (UTRAN) and a User Equipment
(UE). The two general interfaces are the Iu interface, which is
coupled between the UTRAN and the core network, and the radio
interface Uu, which is coupled between the UTRAN and the UE. The
UTRAN consists of several Radio Network Subsystems (RNS). They can
be interconnected by the Iur interface. This interconnection allows
core network independent procedures between different RNSs. The RNS
is further divided into the Radio Network Controller (RNC) and
several base stations (Node-Bs). The base stations are connected to
the RNC by the Iub interface. One base station can serve one or
multiple cells, and typically serves a plurality of UEs. Although
the UTRAN supports both FDD mode and TDD mode on the radio
interface, the present invention is related only to the TDD
mode.
[0004] In the current UMTS TDD systems, the sole criterion for
handover, whether intra- or inter-frequency, is the path loss
difference between the present base station, (i.e., the "serving"
base station), and a target base station. This situation is shown
in FIG. 2. The mobile user equipment (UE) is shown receiving
signals from two base stations: 1) the serving base station
BS.sub.ser; and 2) the target base station BS.sub.tar. The UE
receives the physical channel that carries the broadcast channel
BCH.sub.ser from the serving base station BS.sub.ser and the
physical channel that carries the broadcast channel BCH.sub.tar
from the target base station BS.sub.tar. The UE measures the
strength of the channels BCH.sub.ser, BCH.sub.tar. When the
BCH.sub.tar from the target cell is sufficiently stronger than the
channel BCH.sub.ser from the serving cell, the measurements are
transmitted to the RNC, which determines whether or not to initiate
a handover. Alternatively, measurements can periodically be
signaled to the RNC for the purpose.
[0005] The current procedure 10 carried out by a prior art UMTS TDD
communication system for determining whether to commence handover
can be generally explained with reference to FIG. 3. The UE
receives the physical channel that carries the broadcast channel
(BCH.sub.ser) from the serving base station BS.sub.ser (step 12)
and calculates its strength. The UE also receives the physical
channel that carries the broadcast channel (BCH.sub.tar) from the
target base station BS.sub.tar (step 16) and also calculates its
strength. Periodically, or depending on the relative signal
strengths, the information is signaled to the RNC which determines
the BCH.sub.ser path loss (step 14) and the BCH.sub.tar path loss
(step 18).
[0006] It is then determined whether the BCH.sub.ser path loss is
greater than the BCH.sub.tar pathloss (step 20). If it is not, no
further action is taken. If, however, the BCH.sub.ser path loss is
greater than the BCH.sub.tar path loss as determined by step 20,
the handover to the target base station BS.sub.tar (step 22) is
typically commenced.
[0007] Typically, the values measured at steps 12 and 16 are
transmitted to the RNC, and steps 14, 18 and 20 are performed at
the RNC.
[0008] Although this example illustrates a single target cell, the
same is true for a multiple of target cells of which the UE is
aware, either by detecting their presence or by having received
their parameters from the serving cell.
[0009] In TDD systems that use multi-user detecting (MUD)
receivers, the interference measured in the serving cell is
different from other cells. A prerequisite to receiving data in any
cell is the ability to decode the BCH channel in the cell. Due to
the low spreading factor used in TDD this may be difficult,
particularly at cell edge. Therefore, it would be desirable to
ensure that BCH reception is possible in the target cell prior to
the handover.
[0010] In addition to the path loss, BCH reception depends on the
interference in the slot and prior knowledge of its level is
necessary to determine its likelihood. This is particularly true in
small cells where the interference level is typically higher, and
the interference is also different from cell to cell and UE to UE.
Observing the interference in the serving cell will typically
provide no information about the interference in the target cell
because in the case of a MUD receiver, different slots or different
frequencies may be used. Thus, it would be desirable to measure the
interference in the slot which carries the BCH in the target
cell.
SUMMARY
[0011] The present invention is a method of using a mobile unit in
a multi-cell communication system to determine whether to commence
handover of the mobile unit from a serving base station located in
a first cell of the communication system to a target base station
located in a second cell of the communication system. The mobile
unit determines the serving base station received signal code power
(RSCP.sub.ser), (RSCP the first cell interference signal code power
(ISCP.sub.ser), the target base station received signal code power
(RSCP.sub.tar) and the second cell interference signal code power
(ISCP.sub.tar). If the ratio RSCP.sub.ser/ISCP.sub.ser is less than
the ratio RSCP.sub.tar/ISCP.sub.tar, the mobile unit commences
handover to the target base station. The multi-cell communication
system may be a time division duplex (TDD) system. The mobile unit
may send a message to a radio network controller (RNC) in
communication with the serving and target base stations to initiate
the handover.
[0012] The system utilizes a new criteria and method for initiating
handover between cells. The system measures the downlink
interference in the BCH timeslot, and utilizes this interference in
conjunction with the signal strength as criterion for the handover
decision. The new criterion may be used instead of, or in addition
to, existing criteria.
[0013] Accordingly, the ratio of the signal strength of the BCH to
the interference in the timeslot may be used to make the handover
decision. In one embodiment of the present invention, the signal
strength is used in macro cells where interference is relatively
predictable and BCH reception is easy. The ratio of signal strength
to the interference may be used in pico cells and micro cells.
[0014] An advantage of using both signal strength and interference
measured in the same slot as handover criterion is the inherent
inaccuracy of each of the measurements that results from a use of
an inaccurate automatic gain control (AGC) circuit. As both signal
level and interference are determined at once, their ratio is more
accurate than each alone.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a prior art UTMS system;
[0016] FIG. 2 is a prior art UE receiving the broadcast channel
from two base stations;
[0017] FIG. 3 is the procedure carried out by a prior art UMTS TDD
communication system for determining whether to commence handover;
and
[0018] FIG. 4 is a method for determining whether to institute
handover in accordance with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0019] The present invention will be described with reference to
the drawing figures where like numerals represent like elements
throughout.
[0020] In the following detailed description RSCP refers to the
downlink (DL) reception strength of the broadcast channel (BCH),
which is a measure of the path loss. ISCP refers to the DL
interference in the same slot as observed by the UE receiver.
[0021] In some operating states the mobile decides autonomously on
its serving cell, called autonomous cell selection. The present
invention applies to both network controlled handover and
autonomous cell selection.
[0022] Referring to the flow diagram of FIG. 4, a method 50
including steps for determining whether to institute handover in
accordance with the present invention is shown. The UE first
receives the broadcast channel (BCH.sub.ser) from the serving base
station BS.sub.ser (step 52) and calculates the serving base
station RSCP.sub.ser (step 54). The UE also receives the broadcast
channel BCH.sub.tar from the target base station BS.sub.tar (step
56) and calculates the target base station RSCP.sub.tar (step 58).
The ISCP is then determined for both cells ISCP.sub.ser,
ISCP.sub.tar (step 60). It should be noted that separate ISCP
measurements are needed even if both cells share the same carrier
and slot. The RSCP.sub.ser/ISCP.sub.ser for the serving base
station BS.sub.ser is calculated (step 62), and the
RSCP.sub.tar/ISCP.sub.tar for the target base station is calculated
(step 64). If the RSCP.sub.ser/ISCP.sub.ser for the serving base
station BS.sub.ser is greater than the RSCP.sub.tar/ISCP.sub.tar
for the target base station BS.sub.tar (step 66), then the UE
maintains communications with the serving base station BS.sub.ser.
If, however, the RSCP.sub.ser/ISCP.sub.ser for the serving base
station BS.sub.ser is less than the RSCP.sub.tar/ISCP.sub.tar for
the target base station BS.sub.tar (step 68), the procedure for
handing over to the target base station BS.sub.tar (step 70) is
commenced.
[0023] It should be noted that steps 62, 64, 66, 68 and 70 may be
performed at the RNC or the serving base station BS.sub.ser. In
that case, the UE would forward the ISCP and RSCP measurements to
the RNC or serving base station BS.sub.ser, which would then
perform the calculation steps 62 and 64, comparison steps 66 and
68, and the remaining step 70 of commencing handover to the target
base station BS.sub.tar. Alternatively, the UE may perform steps
62, 64, 66 and 68, and step 70 would comprise sending a message to
the RNC to initiate handover in accordance with prior art handover
methods. It is intended that the present invention operate with
either the UE, RNC, or serving base station BS.sub.ser performing
steps 62, 64, 66, 68, and 70.
[0024] It should be noted that there are many different types of
handover procedures that can be used in accordance with the present
invention, and it is beyond the scope of the present invention to
provide a detailed explanation of such procedures. However, the
present invention provides a new "pre-handover" method for
evaluating whether or not to commence handover.
[0025] It should be noted that this method applies to serving and
target BCHs which are either in the same or different timeslots, or
the same or different frequencies.
* * * * *