EP0948231A2
Expired / Lapsed
EP
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Signal strength triggered handoff in wireless communication systems
Assignee: Alcatel Lucent SAS
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Filing: 1999-03-29
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Granted: —
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Expires: 2019-03-29
Abstract
Abstract An apparatus and method which, in a wireless communication system, improve the quality of inter-frequency hand-offs from an existing call connection frequency to a new frequency by minimizing oscillating inter-frequency hand-offs between the existing call connection frequency and the new frequency, and by minimizing redundant and unnecessary tuning and searching at the new frequency. The present invention accomplishes this improvement by adding specific threshold comparison values (or triggers) within existing messages and through more robust data reporting, from the mobile unit to the base station, when tuning and searching is performed. Particularly, two comparative triggers provided by the present invention avoid unnecessary tuning and searching in the new frequency, thus reducing voice degradation and the risk of dropped calls while pilot searching in the current frequency. Additionally, an alternative embodiment of the present invention compares received power in the new frequency to the received power in the original frequency. If the received power in the new frequency does not exceed the received power in the original frequency by a specified hysteresis threshold value, then a search of the new frequency is unnecessary and the mobile unit "retunes" to the original frequency.
Inventors
- 👤 Wen-Yi Kuo
- 👤 Carl Francis Weaver
- 👤 Martin Howard Meyers
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-24 14:40
CPC Classifications
H; H04; H04W; H04W36/00; H04W36/24; H04W36/30; H04W36/302
Claims Analysis
Total Claims: 32
Claim 1
Independent Claim
81 words
In a wireless communication system having a base station in
communication with a mobile unit at a first frequency, a method for inter-frequency
hand-off of a connected call to a new frequency, said method comprising the steps of: comparing, at said mobile unit, a received power at said first frequency
to a received power threshold value; and tuning said mobile unit to said new frequency if said received power at
said first frequency is less than said received power threshold value.
Claim 2
Dependent Claim
17 words
A method in accordance with claim 1 wherein said wireless
communication system is a CDMA based system.
Claim 3
Dependent Claim
114 words
In a wireless CDMA based communication system having a base station in
communication with a mobile unit at a first frequency, a method for inter-frequency
hand-off of a connected call to a new frequency, said method comprising the steps of: receiving a trigger message at said mobile unit, said trigger message representing
a request for said mobile unit to enable periodic searching and timing at said new
frequency; comparing a received power at said first frequency to a received power threshold
value; and tuning to said new frequency to explore said new frequency for a potential
hand-off opportunity if said received power at said first frequency is less than said
received power threshold value.
Claim 4
Dependent Claim
35 words
A method in accordance with claim 1 or 3 wherein said connected call is continued
at said first frequency if said received power at said first frequency is greater than said
received power threshold value.
Claim 5
Dependent Claim
58 words
A method in accordance with claim 4 further comprising the step of: comparing a summation of active pilot channels' fractional total power to a pilot
power threshold value, wherein said mobile unit continues said connected call at said
first frequency when said summation of active pilot channels' fractional total power is
greater than said pilot power threshold value.
Claim 6
Dependent Claim
52 words
A method in accordance with claim 5 further comprising the step of: transmitting a message report from said mobile unit, said message report
operable to convey a value corresponding to received power at said first frequency and a
value corresponding to each active pilot channel's fractional total power at said first
frequency.
Claim 7
Dependent Claim
45 words
A method in accordance with claim 5 further comprising the step of: tuning to said new frequency to explore said new frequency for a potential hand-off
opportunity if said summation of active pilot channels' fractional total power is less
than said pilot power threshold value.
Claim 8
Dependent Claim
55 words
A method in accordance with claim 7 further comprising the step of: comparing a received power at said new frequency to a new frequency received
power threshold value, wherein said mobile unit tunes to said first frequency if said
received power at said new frequency is less than said new frequency received power
threshold value.
Claim 9
Dependent Claim
36 words
A method in accordance with claim 1 or 8 further comprising the step of: performing a hysteresis check if said received power at said new frequency is
greater than said new frequency received power threshold value.
Claim 10
Dependent Claim
39 words
A method in accordance with claim 9 wherein said hysteresis check is
accomplished by comparing a differential value between said received power at said new
frequency and said received power at said first frequency with a hysteresis threshold
value.
Claim 11
Dependent Claim
44 words
A method in accordance with claim 10 further comprising the step of: tuning to said first frequency when said differential value between said received
power at said new frequency and said received power at said first frequency is less than
said hysteresis threshold value.
Claim 12
Dependent Claim
66 words
A method in accordance with claim 11 further comprising the step of: transmitting a message report from said mobile unit, said message report
operable to convey: a value corresponding to said received power at said first frequency, a value corresponding to said received power at said new frequency, and a value corresponding to at least one active pilot channel's fractional total
power at said first frequency.
Claim 13
Dependent Claim
47 words
A method in accordance with claim 10 further comprising the step of: performing an inter-frequency hand-off to said new frequency when said
differential value between said received power at said new frequency and said received
power at said first frequency is greater than said hysteresis threshold value.
Claim 14
Dependent Claim
84 words
A method in accordance with claim 13 further comprising the step of: transmitting a message report from said mobile unit, said message report
operable to convey a value corresponding to said received power at said first frequency, a value corresponding to said received power at said new frequency, a value corresponding to said at least one active pilot channel's fractional
total power at said first frequency, and a value corresponding to at least one active pilot channel's fractional total
power at said new frequency.
Claim 15
Dependent Claim
122 words
In a wireless CDMA based communication system having a base station in
communication with a mobile unit at a first frequency, a method for inter-frequency
hand-off of a connected call to a new frequency, said method comprising the steps of: receiving a General Handoff Direction Message (GHDM) at said mobile unit,
said GHDM being a trigger message causing said mobile unit to enable periodic
searching and tuning at said new frequency; comparing a received power at said first frequency to a SF_RX_PWR_THRESH
value, said SF_RX_PWR_THRESH value being a received power threshold value; and tuning to said new frequency to explore said new frequency for a potential
hand-off opportunity if said received power at said first frequency is less than said
SF_RX_PWR_THRESH value.
Claim 16
Dependent Claim
31 words
A method in accordance with claim 15 wherein said connected call is continued
at said first frequency is said received power at said first frequency is greater than said
SF_RX_PWR_THRESH value.
Claim 17
Dependent Claim
58 words
A method in accordance with claim 16 further comprising the step of: comparing a summation of active pilot channel's fractional total power to a pilot
power threshold value, wherein said mobile unit continues said connected call at said
first frequency when said summation of active pilot channels' fractional total power is
greater than said pilot power threshold value.
Claim 18
Dependent Claim
55 words
A method in accordance with claim 17 further comprising the step of: transmitting a Candidate Frequency Search Report Message (CFSREPM) from
said mobile unit, said CFSREPM operable to convey a value corresponding to received
power at said first frequency and a value corresponding to each active pilot channel's
fractional total power at said first frequency.
Claim 19
Dependent Claim
45 words
A method in accordance with claim 17 further comprising the step of: tuning to said new frequency to explore said new frequency for a potential hand-off
opportunity if said summation of active pilot channel's fractional total power is less
than said pilot power threshold value.
Claim 20
Dependent Claim
58 words
A method in accordance with claim 19 further comprising the step of: comparing a received power at said new frequency to a CF_RX_PWR_THRESH
value, said CF_RX_PWR_THRESH value being a new frequency received power
threshold value, wherein said mobile unit tunes to said first frequency if said received
power at said new frequency is less than said CF_RX_PWR_THRESH value.
Claim 21
Dependent Claim
30 words
A method in accordance with claim 20 further comprising the step of: performing a hysteresis check if said received power at said new frequency is
greater than said CF_RX_PWR_THRESH value.
Claim 22
Dependent Claim
45 words
A method in accordance with claim 21 wherein said hysteresis check is
accomplished by comparing a diiferential value between said received power at said new
frequency and said received power at said first frequency with a
DIFF_RX_PWR_THRESH value, said DIFF_RX_PWR_THRESH value being
hysteresis threshold value.
Claim 23
Dependent Claim
43 words
A method in accordance with claim 22 further comprising the step of: tuning to said first frequency when said differential value between said received
power at said new frequency and said received power at said first frequency is less than
said DIFF_RX_PWR_THRESH value.
Claim 24
Dependent Claim
69 words
A method in accordance with claim 23 further comprising the step of: transmitting a Candidate Frequency Search Report Message (CFSREPM) from
said mobile unit, said CFSREPM operable to convey: a value corresponding to said received power at said first frequency, a value corresponding to said received power at said new frequency, and a value corresponding to at least one active pilot channel's fractional total
power at said first frequency.
Claim 25
Dependent Claim
46 words
A method in accordance with claim 22 further comprising the step of: performing an inter-frequency hand-off to said new frequency when said
differential value between said received power at said new frequency and said received
power at said first frequency is greater than said DIFF_RX_PWR_THRESH value.
Claim 26
Dependent Claim
87 words
A method in accordance with claim 25 further comprising the step of: transmitting a Candidate Frequency Search Report Message (CFSREPM) from
said mobile unit, said CFSREPM operable to convey: a value corresponding to said received power at said first frequency, a value corresponding to said received power at said new frequency, a value corresponding to said at least one active pilot channel's fractional
total power at said first frequency, and a value corresponding to at least one active pilot channel's fractional total
power at said new frequency.
Claim 27
Dependent Claim
120 words
In a wireless communication system having a plurality of base stations including
active set base stations using a first frequency for communicating with a mobile unit, a
method for inter-frequency hand-off from the first frequency to a second frequency, the
method comprising the steps of: comparing a first received power at the mobile unit for signals transmitted by
base stations in the wireless communication system using the first frequency to a first
received power threshold value; and tuning the mobile unit to the second frequency to measure a second received
power for signals transmitted by base stations using the second frequency if the first
received power at the first frequency is not greater than the first received power
threshold value.
Claim 28
Dependent Claim
54 words
A method of claim 27 comprising the additional step of: comparing a summation of received powers at the mobile unit for signals
transmitted by the active set base stations using the first frequency to a second received
power threshold value if the first received power is greater than the first received power
threshold value.
Claim 29
Dependent Claim
37 words
A method of claim 28, wherein the step of comparing the summation of
received powers comprises the step of: measuring received powers for pilot channel signals transmitted by the active set
base stations using the first frequency.
Claim 30
Dependent Claim
74 words
A method of claim 28, wherein the mobile unit maintains communication with
the active set base stations if the summation of received powers is greater than the
second received power threshold value, and the mobile unit tunes to the
second frequency to measure the second received power for signals
transmitted by the base stations using the second frequency if
the summation of received powers is not greater than the second
received power threshold value.
Claim 31
Dependent Claim
62 words
The method of claim 27 comprising the additional steps of: measuring the second received power for signals transmitted by base stations
using the second frequency when the mobile unit is tuned to the second frequency, and determining whether there are any active set base stations using the second
frequency if the received power difference value is greater than the hysteresis threshold
value.
Claim 32
Dependent Claim
62 words
The method of claim 27 comprising the additional steps of: comparing a received power difference value to a hysteresis threshold value, the
received power difference value being a difference between the second received power
and the first received power, and tuning the mobile unit to the first frequency if the received power difference value
is not greater than the hysteresis threshold value.
References Cited (Backward Citations)
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