U.S. patent application number 09/324177 was filed with the patent office on 2001-11-15 for macrodiversity control system having macrodiversity mode based on operating category of wireless unit.
Invention is credited to RAHMAN, MOHAMED ANISUR.
Application Number | 20010041569 09/324177 |
Document ID | / |
Family ID | 23262438 |
Filed Date | 2001-11-15 |
United States Patent
Application |
20010041569 |
Kind Code |
A1 |
RAHMAN, MOHAMED ANISUR |
November 15, 2001 |
MACRODIVERSITY CONTROL SYSTEM HAVING MACRODIVERSITY MODE BASED ON
OPERATING CATEGORY OF WIRELESS UNIT
Abstract
A macrodiversity control system provides a wireless unit with a
macrodiversity mode depending on the operating category of the
wireless unit. For example, a wireless communications system can
have wireless units operating in categories related to the mobility
of the wireless unit, such as fixed, limited fixed (mobility within
the home cell) and/or fully mobile. For a wireless unit, the
macrodiversity mode of the wireless unit can be established
depending on the operating category for the wireless unit. Where
the wireless unit is fixed and has good reception from a home base
station, particularly in regions close to the home base station,
macrodiversity for the wireless unit can be restricted. Because the
mobility of the wireless unit is restricted in the fixed (or
limited fixed) mode, the fading of signals between the home base
station and the wireless unit should not be severe, thereby
macrodiversity is disabled. Where the reception is poor,
particularly in a region near the edge of the cell, the
macrodiversity for the fixed (or limited fixed) wireless unit is
enabled. The fixed (or limited fixed) wireless unit at the edge of
the cell can benefit from macrodiversity, but because the wireless
unit is fixed (or limited fixed), the fixed (or limited fixed)
wireless unit is not handed off to another base station (or can
only be handed off to a limited set of base stations).
Inventors: |
RAHMAN, MOHAMED ANISUR;
(RANDOLPH, NJ) |
Correspondence
Address: |
Birch Stewart
Kolasch & Birch LLP
P O Box 747
Falls Church
VA
22040-0747
US
|
Family ID: |
23262438 |
Appl. No.: |
09/324177 |
Filed: |
June 3, 1999 |
Current U.S.
Class: |
455/436 ;
455/277.1; 455/504 |
Current CPC
Class: |
H04B 7/022 20130101;
H04W 36/18 20130101; H04W 84/14 20130101; H04B 7/0491 20130101 |
Class at
Publication: |
455/436 ;
455/277.1; 455/504 |
International
Class: |
H04Q 007/20 |
Claims
1. A method of communicating within a wireless communications
system including a base station and a wireless unit, said method
comprising: operating said wireless unit in a macrodiversity mode
depending on an operating category for said wireless unit and said
operating category related to the mobility of said wireless
unit.
2. The method of claim 1 wherein said operating comprising:
operating said wireless unit in said macrodiversity mode depending
on said wireless unit operating as fixed and on the quality of
reception from said base station.
3. The method of claim 2 wherein said operating including:
disabling macrodiversity for said wireless unit if the quality of
reception from said base station is above a threshold.
4. The method of claim 2 wherein said operating including: enabling
macrodiversity for said wireless unit if the quality of reception
from said base station is below a threshold.
5. The method of claim 4 further including: disabling handoffs for
said wireless unit.
6. The method of claim 5 wherein said disabling further including:
setting handoff parameters for said wireless unit.
7. The method of claim 5 further including: blocking handoff
messages for said wireless unit.
8. The method of claim 5 further including: switching said wireless
unit from said fixed category to a limited fixed category; and
operating said wireless unit in a limited fixed macrodiversity mode
for said wireless unit.
9. The method of claim 5 further including: switching said wireless
unit from said fixed category to a mobile category; and operating
said wireless unit in a mobile macrodiversity mode for said
wireless unit.
10. The method of claim 9 further including: enabling handoffs for
said wireless unit.
11. The method of claim 2 further including: storing a home cell id
associated with the home base station of said wireless unit; and
using said home cell id in accessing said wireless communications
system.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of The Invention
[0002] This invention relates to wireless communications and, more
particularly, to a cellular communications system with wireless
units of different operating categories.
[0003] 2. Description of Related Art
[0004] FIG. 1 depicts a diagram of a portion of a typical wireless
communications system 10, which provides wireless communications
service to a number of wireless or mobile units 12a-c, that are
situated within a geographic region. The geographic region serviced
by a wireless communications system is divided into spatially
distinct areas called "cells." Each cell is schematically
represented by one hexagon in a honeycomb pattern; in practice,
however, each cell has an irregular shape that depends on the
topography of the terrain surrounding the cell and other factors. A
conventional cellular telephone system comprises a number of cell
sites or base stations 14a-d, geographically distributed to support
transmission and receipt of voice-based communication signals to
and from cellular telephones, often referred to as mobile units or
wireless units. Each cell site handles voice communications over a
cell, and the overall coverage area for the cellular telephone
system is defined by the union of cells for all of the cell sites,
where the coverage areas for nearby cell sites overlap to some
degree to ensure (if possible) contiguous communications coverage
within the outer boundaries of the system's coverage area. One cell
site may sometimes provide coverage for several sectors. In this
specification, cells and sectors are referred to
interchangeably.
[0005] A base station 14a-d comprises the radios and antennas that
the base station uses to communicate with the mobile units in that
cell and also comprises the transmission equipment that the base
station uses to communicate with a Mobile Switching Center (MSC)
16. The Mobile Switching Center 16 is responsible for, among other
things, establishing and maintaining calls between the mobile units
and calls between a mobile unit and a wireline unit (e.g., wireline
unit 18), which wireline unit 18 is connected to the Mobile
Switching Center (MSC) 16 via a public switched telephone network
(PSTN) 20. The Mobile Switching Center 16 is connected to a
plurality of base stations, such as base stations 14a-d, that are
dispersed throughout the geographic region serviced by the MSC 16
and to the PSTN 20 and/or a packet data network (PDN) 22, such as
the Internet. The MSC 16 is connected to several databases,
including a home location register (HLR) 24. The HLR 24 contains
subscriber information and location information for all mobile
units which reside in the geographic region of the MSC 16.
Typically, for each of the mobile units, the HLR 24 stores a mobile
identification number (MIN) or International Mobile Subscriber
Identification Number (IMSI), the mobile directory or phone number
(MDN), and/or an electronic serial number (ESN).
[0006] When active, a mobile unit receives forward-link signals
from and transmits reverse-link signals to (at least) one cell site
or base station. Each active mobile unit is assigned a forward link
on which it receives its forward-link signals on at least one
forward link channel and a reverse link on which it transmits
reverse link signals on at least one reverse link channel. There
are many different schemes for defining forward and reverse link
channels for a cellular telephone system, including TDMA
(time-division multiple access), FDMA (frequency-division multiple
access), and CDMA (code-division multiple access) schemes. In CDMA
communications, different channels are distinguished by different
spreading sequences that are used to encode different voice-based
streams, which may then be modulated at one or more different
carrier frequencies for simultaneous transmission. A receiver can
recover a particular voice-based stream from a received signal
using the appropriate spreading sequence to decode the received
signal.
[0007] In order to avoid interference between signals transmitted
to and from mobile units in a CDMA system, all active mobile units
within a particular cell are assigned different CDMA spreading
sequences. Since cellular telephone systems are dynamic systems in
which mobile units become active and inactive at different (and
possibly random) times and since mobile units can move from one
cell to another, the assignment of channels to the various mobile
units is made by the cellular system in real time. In order to
assign bandwidth resources to mobile units so as to avoid
interference between mobile units in neighboring cells, the
resource-assignment activities of neighboring cell sites are
coordinated.
[0008] A detailed sequence of activities are typically followed
before the mobile unit can access the wireless communications
system to establish or receive a call. As is known in the art,
calls between a CDMA mobile unit and a base station typically
employ several kinds of channels. Initially, a pilot channel is
employed to continually broadcast certain system synchronization
and timing information to all mobile units in an area. After
initial synchronization is achieved at a mobile unit, a sync
channel is used to establish more specific time and frame
synchronization at the mobile unit. The sync channel message also
provides information about another class of channels, the paging
channels. Paging channels are used to broadcast a variety of
control information, including access channel information,
contained in the access parameter message. This access parameter
message contains parameters and other information of interest to
mobile units seeking access to the base station. Other overhead
messages are sent between the mobile unit and the base station to
facilitate communications over forward and reverse link traffic
channels between the mobile unit and the base station over which
voice and/or data information is transmitted.
[0009] Conventional CDMA systems being developed use macrodiversity
to improve the performance or quality of reception. The
macrodiversity concept as is used in CDMA involves two or more
simultaneous links from two or more base stations. The mobile and
cell receivers employ a number of parallel correlators. Receivers
using parallel correlators (sometimes called RAKE receivers) allow
individual path arrivals to be tracked independently and the sum of
their received signal strengths is then, used to demodulate the
signal. While there is fading on each arrival, the fades are
independent. Demodulation based on sum of the signals is then much
more reliable. But in this process it might use a lot of
resources/equipment of a cell site. Moreover, it is expected that
quite a high percentage of the calls will use macrodiversity.
[0010] Once a system is designed, the number of transceiver
elements are fixed, and as the number of users increase,
macrodiversity will use up the wireless resources. For the
macrodiversity to operate, the mobile unit searches for pilot
signals of base stations on a candidate list which are not
currently servicing the wireless unit. The wireless unit measures
the signal strengths, for example using a received signal strength
indicator (RSSI) of the pilot signals. When the wireless unit
detects a pilot of sufficient strength which is associated with a
base station not assigned to the wireless unit, a pilot measurement
message including the pilot signal measurements is provided to the
MSC 16. Using the pilot signal measurements, the MSC 16 determines
whether to assign a traffic channel from another base station to
the wireless unit. The wireless unit is said to be in
macrodiversity state if it is assigned traffic channels from more
than one base station. Within the geographic region, the MSC 16
switches calls from one base station to another in real time as the
mobile unit moves between cells, referred to as call handoff.
[0011] All base stations connected to a given wireless unit define
the active set of that mobile, and an active set update function
controls, i.e, evaluates and updates, this active set based on
pilot strength measurements. At the wireless unit, the strongest
pilots are detected and measured by the measurement process. The
signal strength values are then collected into the pilot
measurement report, which is sent to the MSC 16. When the active
set update function is invoked, the base stations within the active
set from which the strongest and weakest pilot are received are
identified. If the difference is greater than the system desired
value (called active set window there after), the weakest base
station will be removed from the active set. A base station is
added to the active set window, if it received pilot signal
strength is within the window above an active set threshold value,
provided the active set size (no. of RAKE fingers in the receiver)
is not exceeded. If the active set size is full, the weakest base
station in the active set will be replaced by the new base station
if the corresponding pilot signal strength is higher than the
weakest base station.
[0012] Some wireless cellular communications systems involve fixed
wireless units. The fixed cellular concept is getting a lot of
attention and is a substitute for the public switched telephone
network (PSTN), where the terrain is difficult and the
infrastructure cost is too high to implement the PSTN. The fixed
cellular concept involves wireless units where the mobility of the
wireless unit is very limited within the home cell (limited or no
mobility at all). Macrodiversity is not normally used and no
handoffs are allowed between the base stations.
[0013] Macrodiversity as used in the CDMA system has the advantage
that it improves the quality of reception in the cellular or PCS
system, but if the cellsite is fully loaded (all the transceivers
are being used up), the capacity of the system suffers. Thus,
macrodiversity needs to be coordinated, especially in a system
using both fixed and mobile units, to more efficiently use the
resources of the wireless communications system.
SUMMARY OF THE INVENTION
[0014] The present invention involves a macrodiversity control
system, for a wireless communication system, which provides a
wireless unit using a macrodiversity mode depending on the
operating category of the wireless unit. For example, a wireless
communications system can have wireless units operating in
categories related to the mobility of the wireless unit, such as
fixed, limited fixed (mobility within the home cell) and/or fully
mobile. For a wireless unit, the macrodiversity mode of the
wireless unit can be established depending on the operating
category for the wireless unit. Where the wireless unit is fixed
and has good reception from a home base station, particularly in
regions close to the home base station, macrodiversity for the
wireless unit can be restricted. Because the mobility of the
wireless unit is restricted in the fixed (or limited fixed) mode,
the fading of signals between the home base station and the
wireless unit should not be severe, thereby macrodiversity is
disabled. Where the reception is poor, particularly in a region
near the edge of the cell, the macrodiversity for the fixed (or
limited fixed) wireless unit is enabled. The fixed (or limited
fixed) wireless unit at the edge of the cell can benefit from
macrodiversity, but because the wireless unit is fixed (or limited
fixed), the fixed (or limited fixed) wireless unit is not handed
off to another base station (or can only be handed off to a limited
set of base stations).
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Other aspects and advantages of the present invention may
become apparent upon reading the following detailed description and
upon reference to the drawings in which:
[0016] FIG. 1 shows a general diagram of a cellular communications
system in which the wireless communications system according to the
principles of the present invention can be used;
[0017] FIG. 2 shows a diagram of a cellular system using the
principles of the present invention; and
[0018] FIG. 3 shows a flow diagram of an embodiment of the
macrodiversity control system according to the principles of the
present invention.
DETAILED DESCRIPTION
[0019] Illustrative embodiments of the macrodiversity/handoff
control system ("macrodiversity control system") are described with
respect to a cellular system of wireless units having different
operating categories, such as fixed (no mobility), limited fixed
(limited fixed mobility within the home cell) and/or fully mobile
wireless units. In some embodiments, the wireless unit can switch
between fixed, limited fixed and/or mobile categories. FIG. 2 shows
a base station 30 for a cell 32. For illustrative purposes, the
cell 32 is shown with a macrodiversity region 34 and a
non-macrodiversity region 36 for wireless units in the fixed
category. In the fixed operating category, wireless units can be
rigidly fixed, such as a wireless unit 40 with an antenna on the
roof directed towards the base station. In such a case, the antenna
has a fairly high height gain, and the directional antenna helps
reception. Since the position of the antenna is known, the
macrodiversity/handoff mode or operation of the wireless unit can
be established and set during installation/RF optimization by
adjusting the antenna position or direction.
[0020] In some embodiments, a limited fixed operating category can
be established where mobility is restricted (for example, a limited
fixed wireless unit may be limited to walking speed because the
wireless unit is in a home or premises), as such the fading
scenarios are not as severe as a fully mobile wireless unit. For
the limited fixed category, wireless units can operate using a
different macrodiversity mode or operation than the mode used by
the fixed wireless units. For example, a dashed line 37 can
designate a boundary between the macodiversity and
non-macrodiversity regions for the limited fixed category. The
different macrodiversity regions can be defined by macrodiversity
triggering values used by the macrodiversity control system in
comparisons with signal quality measurements, such as the signal
strength measurements of the forward and/or reverse traffic or
pilot channels to determine the macrodiversity mode for the
wireless unit. In alternative embodiments, the
macrodiversitry/handoff operation for a particular wireless unit is
determined by individual macrodiversity trigger values and/or
handoff threshold values for the particular wireless unit. The
operating category for the wireless unit can be the basis for
establishing the macrodiversity/handoff operation for the wireless
unit.
[0021] The macrodiversity mode for the wireless unit can be
established at subscription or installation/RF optimization and
maintained, or in some embodiments, the macrodiversity/handoff mode
of the wireless unit can be changed, for example based on a change
in operating category or a change by the system in how the
macrodiversity modes for particular operating categories,
particular mobiles, particular cells or the system are defined.
Furthermore, the macrodiversity mode of the wireless unit can be
determined using certain operating parameter(s), such as signal
quality measurements of signal to and/or from the base station
and/or the traffic load of the cell and/or surrounding cells. Prior
traffic patterns and/or prior handoff or macrodiversity
characteristics for the wireless unit can also be used to determine
the macrodiversity operation for the wireless unit. For example,
the wireless unit can be in a macrodiversity region in the summer
and a non-macrodiversity region in the winter. Depending on the
embodiment, the boundary 37 can change.
[0022] In the macrodiversity region 34, a fixed wireless unit 38
has macrodiversity enabled because the reception from the base
station 30 is poor, for example below a fixed macrodiversity
trigger value, such as a signal quality value measured by signal
strength, signal to noise ratio (such as Ec/Io), bit error rate
(BER), and/or frame error rate (FER). The macrodiversity region 34
is typically at the edge of the cell 32 or in a hand off region,
but can extended for a wireless unit with poor reception due to
location or other interference scenarios (although physically close
to the base station 30 such as area 39). When macrodiversity is
enabled, the wireless unit 38 can receive signals from the base
stations of other cells to improve reception, but the wireless unit
38 will not be handed off to the other cells when in a fixed
operating category. In certain embodiments, the fixed wireless unit
can use macrodiversity without being handed off to another cell by
blocking or bypassing the handoff procedure, for example by
blocking a hand off parameter measurement request message and/or a
hand off direction message for the fixed wireless unit 38 used in a
typical system to initiate a handoff.
[0023] Alternatively, handoff parameter values or thresholds used
to initiate handoff procedures in comparisons with signal quality
measurements of received signals from the serving and/or other base
stations can be set on a per wireless unit basis to prevent the
wireless unit from being handed off and/or to be handed off only
under limited conditions, such as when the wireless unit is in a
limited fixed mode and receiving signals below a threshold value
different from the threshold value determining a handoff for a
mobile wireless unit. In such a scenario, a restricted list of
candidate base stations can be examined for macrodiversity and/or
handoffs, and the active set could be limited when compared to a
fully mobile wireless unit. Another parameter to determine whether
a fixed (or limited fixed) wireless unit can enable macrodiversity
and/or handoffs is the load on the cell 32 and/or of the
surrounding cells. For example, when the traffic load is below a
threshold, macrodiversity and/or handoffs can be enabled by setting
the active set threshold values and/or handoff related parameters
to enable macrodiversity and/or handoffs.
[0024] A fixed (or limited fixed) wireless unit 40 or 42 has
macrodiversity disabled in a non-macrodiversity region 36 where the
reception is good from the serving base station 30, for example
above a fixed (or limited fixed) macrodiversity threshold value,
such as a signal quality measurement value of a signal from the
serving base station 30, for example a measurement of signal
strength, frame error rate (FER), or bit error rate (BER). Such a
non-macrodiversity region 36 is typically close to the base station
30 but can be extended to areas, such as area 43, where the
wireless unit has good reception although located close to the edge
of the cell. By properly coordinating the macrodiversity region
(where macrodiversity between different cells and sites are allowed
as shown in FIG. 2), wireless resources can be used more
efficiently. Establishing the wireless unit 40 or 42 as fixed and
operating with macrodiversity disabled saves wireless system
resources, such as traffic channels which would be used for
macrodiversity as well as resources required in registering
wireless units with other base stations. Additionally, the
interference in the wireless system is reduced due to the avoidance
of multiple base stations transmitting the same information. Even
if macrodiversity is enabled, active set threshold values, a
restricted or limited active set(s) and/or other
macrodiversity/handoff parameters could be used for macrodiversity
while handoffs are prevented (or limited).
[0025] In certain embodiments, a wireless unit 40 or 42 can be
designated as fixed and assigned a home cell 32 where calls are to
be originated. When the wireless unit 40 or 42 attempts to gain
access to the wireless system, the macrodiversity control system
can retrieve a home cell identification corresponding to the
wireless unit 40 or 42. The home cell identification can be
retrieved from the home location register 24 (FIG. 1) of the MSC 16
(FIG. 1) and/or from the wireless unit. If access is attempted by
the wireless unit 40 or 42 (in the fixed or limited fixed mode) at
some other base station 30, the system can respond with a directed
retry message. The base station 30 can send a directed retry
message to instruct the wireless unit that service is not supported
in the cell where access was attempted and try access elsewhere or
with different operating category or parameters. The system could
simply deny access to the wireless unit, or change the operating
category of the wireless unit from fixed or limited fixed to
mobile.
[0026] In a wireless system with fixed (no mobility at all),
limited fixed (mobility within the home cell) and fully mobile
units, the wireless units can be designated at subscription as
fixed or limited fixed within the home cell. As such, the fixed or
limited fixed wireless units will not have to register with the
base station 30. Registration is the process by which the wireless
unit notifies the base station of its location, and identification
so that the base station can page the base station when
establishing a wireless terminated call. For example, in American
National Standards (ANSI) J-STD-008 dated Mar. 24, 1995 entitled
Personal Station-Base Station Compatibility Requirements for 1.8 to
2.0 GHz Code Division Multiple Access (CDMA) Personal
Communications Systems (ANSI J-STD-008), various forms of
registration are described. Fixed (or limited fixed) wireless units
will always be registered with the same home cell, thereby
relieving the wireless system of registration-related processing
which is very significant in a cellular environment. For the
wireless units designated as filly mobile, the registration should
be handled and processed as described in current standards, such as
ANSI J-STD-008.
[0027] As such, the fixed (or limited fixed) wireless unit can be
charged at a discount rate because the fixed units will need less
system capability and resources than a mobile wireless unit. At
call origination, page response or registration by the wireless
unit, the system can determine the operating category or
macrodiversity mode of the wireless unit (fixed, limited fixed or
mobile). The macrodiversity control system can determine the mode
for the wireless unit by receiving the operating category from the
wireless unit and/or by retrieving the operating category and/or
macrodiversity mode for the wireless unit from a database
accessible to the macrodiversity control system. For example, the
current operating category and/or the macrodiversity mode, which is
determined or defined by the macrodiversity trigger values, active
set threshold values, limited or restricted active set, limited or
restricted candidate set and/or the handoff thresholds or
parameters can be stored in a database accessible to the MSC 16 of
the base station 30, such as the HLR 24 (FIG. 1). The wireless unit
operating category and/or macrodiversity mode or parameters thereof
can be stored in other databases, such as a stand-alone HLR (SHLR).
The operating category and/or macrodiversity mode and parameters
thereof can be stored in association with a wireless unit, in
association with the operating category and/or in association with
the home cell id. The home cell id and/or the operating category
can be stored in association with the wireless unit and the
corresponding macrodiversity modes and parameters thereof can be
stored in association with operating category and/or home cell
id.
[0028] In some embodiments, the capability of the wireless unit is
established at subscription or installation/RF optimization and
maintained. In other embodiments, the wireless unit can switch
between the fixed, limited fixed and/or mobile modes. For example,
the wireless unit could plug into a docking station which includes
a wireless network interface unit (NIU), including amplification
circuitry, connected to an antenna, such as an antenna on the roof
of a house. When engaged with the docking station, the wireless
unit can be in the fixed operating category using the fixed
macrodiversity mode defined by the fixed macrodiversity trigger
values, active set thresholds, active set or candidate set, other
parameters and/or by whether handoffs are prevented for the
particular fixed wireless unit configuration or for those fixed
wireless units in the cell. When engaged with the docking station,
the amplification and antenna circuitry in the wireless unit can be
bypassed by the network interface unit (NIU) circuitry and antenna
connected to the docking station. When the wireless unit is
disengaged from the docking station, the wireless unit can use
amplification circuitry and the antenna integrated with the
wireless unit and switch to a limited fixed operating category by
sending a message to the base station. Alternatively, a switch on
the wireless unit can change the operating category for the
wireless unit. Depending on the embodiment, the macrodiversity
control system can be capable of changing the operating category of
the wireless unit 40 from fixed (or limited fixed) to mobile,
whereby the wireless unit 40 can be handed off between base
stations when the wireless unit 40.
[0029] Alternatively, at system access, the wireless unit can send
in a message to the base station a home cell id and/or operating
category for the wireless unit. If the home cell id and the base
station at which access to the wireless communications system is
being requested match, then the wireless unit remains in the fixed
(or limited fixed) operating category. Otherwise, depending on the
embodiment, the base station can change the operating category for
the wireless unit or the wireless unit requests a category change
if a home cell id stored in the wireless unit or at the HLR 15 does
not match a home cell of the base station at which access to the
system is being attempted. For example, in one embodiment, the
macrodiversity control system or portion thereof receives at the
wireless unit a home cell id of the base station to compare with
the home cell id stored at the wireless unit. In ANSI J-STD-008 ,
the Access Parameter Message (APM) sent over the access channel
from the base station to the wireless unit can be modified to
include a field called the home cell ID. In other embodiments, the
wireless unit simply identifies itself (from which the
macrodiversity control system obtains the home cell id of the
wireless unit) or provides its home cell id to the base station and
the home cell id associated with the wireless unit is compared with
the home cell id of the base station which the wireless unit is
attempting to access. If the home cell id associated with the
wireless unit matches the home cell id of the base station being
accessed, the operating category can remain as fixed (or limited
fixed). If not, the operating category for the wireless unit can be
changed to fully mobile.
[0030] In response to any change in operating category, the
macrodiversity mode for the wireless unit can change. Accordingly,
depending on the embodiment, the base station can send
corresponding macrodiversity trigger values, active set thresholds,
limited, fixed or restricted candidate list, limited, fixed or
restricted active set and/or other macrodiversity and handoff
parameters or thresholds. Once the mode is changed, different
macrodiversity and/or handoff thresholds can be used.
Alternatively, if mode changes are not permitted by the wireless
system, the call could be dropped. In cellular systems described
herein, the charges for the wireless unit 40 can be cheaper when
operating in fixed (no mobility) mode or limited fixed (mobility
restricted within the home cell) than in mobile mode. The use of
macrodiversity modes depending on the operating category, and the
corresponding parameters, thresholds, candidate lists, procedures,
values and/or other information or macrodiversity/handoff
processes, can be used on a wireless unit basis, on a cell-wide
basis or on a system wide basis.
[0031] Thus, the fixed wireless communications system enables
increased capacity in a wireless communications system of fixed,
limited fixed and/or mobile units by more efficiently using
wireless resources for the wireless system. The fixed wireless
system can be used for improving the performance of a stand-alone
fixed wireless system or a mixed wireless system having fixed (or
limited fixed) wireless units and mobile wireless units.
[0032] FIG. 3 shows a flow diagram of an embodiment of the
macrodiversity control system depending on the operating categories
of fixed, limited fixed or mobile for the wireless unit. More or
less operating categories for the wireless units are possible. At
block 50, the macrodiversity control system determines the
operating category for the wireless unit. The operating category
for the wireless unit can be established at subscription or
installation and stored at the wireless unit and/or in the wireless
communications system in association with the subscriber
information of the wireless unit, such as electronic serial number,
mobile identification number (MIN or IMSI) and directory or phone
number (DN). Additionally, a home cell id can be stored at the HLR
24 (FIG. 1) and/or in the wireless unit. Depending on the
embodiment, the macrodiversity control system and portions thereof
can be implemented at the wireless unit and/or in the wireless
communications system, such as the base station and/or the MSC 16
(FIG. 1)
[0033] The macrodiversity control system can be informed of the
operating category for the wireless unit (fixed, limited fixed or
mobile), for example in a message to the base station and/or a
message from the base station to the wireless unit. The operating
category (and corresponding macrodiversity/handoff mode parameters)
for the wireless unit can be stored in the wireless unit and/or in
the wireless communications system, for example in the base station
or HLR 24. Depending on the embodiment, the operating category
and/or macrodiversity/handoff mode can be maintained until a change
in the subscription occurs. Moreover, in some embodiments, the
operating category and/or the macrodiversity/handoff mode and the
parameters thereof can be updated periodically, dynamically or
depending on other operating parameters, such as received signal
strength of a channel on the reverse and/or forward links. As such,
the macrodiversity control system can determine the operating
category and/or macrodiversity mode for the wireless unit at every
attempt to access the wireless system by the wireless unit or
established initially and maintained. Other embodiments are
possible.
[0034] At block 52, the macrodiversity control system determines
whether the wireless unit is in a fixed operating category. If the
wireless unit is operating as a fixed unit, the macrodiversity
control system determines macrodiversity trigger values for
wireless units operating as fixed or for that particular wireless
unit as shown in block 54. The macrodiversity trigger value can be
different for each wireless unit or for each operating category.
Depending on the macrodiversity mode and/or other parameters
related to the home cell, such as traffic load of the cell or
surrounding cells, and/or the wireless unit, such as signal quality
or speed of the wireless unit, as well as other parameters, the
macrodiversity control system can set the macrodiversity trigger
levels. After the macrodiverity trigger value is determined, the
macrodiversity control system establishes the macrodiversity mode
for the wireless unit.
[0035] In the embodiment of FIG. 3, the macrodiversity/handoff
control system performs a signal quality measurement using for
example a received signal strength indicator (RSSI) at the wireless
unit. If the macrodiversity trigger is less than the signal
strength measurement at block 56, the macrodiversity for the
wireless unit is disabled as shown at block 58. Depending on the
embodiment, from the system side, transmission to a particular
wireless unit can be limited to the serving base station.
Macrodiversity can be disabled by restricting the active set to the
serving base station, for example by setting active set threshold
values or other parameters at RF optimization relative to the home
base station. As such, the wireless unit can only communicate with
the home base station. If the macrodiversity trigger value is
greater than the signal strength measurement at block 56,
macrodiversity is enabled. As shown in block 60, active set
threshold values for the wireless unit and/or a restrictive or
limited set of candidate base stations, for example of certain
cells neighboring the home cell, can be established for the
wireless unit. With macrodiversity enabled, the wireless unit can
receive signals from the base stations on the active sets but will
not be handed off from the home base station. As such, handoffs are
disabled. The macrodiversity/handoff control system can accomplish
this in different ways, for example by preventing the wireless unit
from requesting handoffs, ignoring handoff requests and/or setting
handoff parameters to achieve desired operation. Depending on the
embodiment, the trigger values, active set threshold values and/or
handoff parameters can be the same and/or different.
[0036] Besides a fixed operating category, the macrodiversity
control system can include additional operating categories, such as
limited fixed, fully mobile and others, for example categories
based on speed. As previously mentioned, the operating category can
be established at subscription or installation and maintained or
changed, for example from fixed to limited fixed by removing the
wireless unit from a fixed docking station or by using a switch on
the wireless unit to switch between operating categories.
[0037] In any event, if at block 52, the macrodiversity control
system determines that the operating category of the wireless unit
is not fixed, the macrodiversity control system determines at block
62 whether the operating category of the wireless unit is limited
fixed. If not, the wireless unit operates as a fully mobile
wireless unit operating for example as described in ANSI J-STD-008
with handoffs and macrodiversity enabled as shown in block 64.
Otherwise, if the control system determines that the wireless unit
is operating as limited fixed, the control system determines at
block 66 the macrodiversity trigger value for the wireless unit.
Depending on the embodiment, the macrodiversity trigger value for
the limited fixed wireless unit can be the same or different than
the macrodiversity trigger value of the fixed wireless unit or of
other limited fixed wireless units.
[0038] At block 68, the control system compares the limited fixed
macrodiversity trigger value with a signal quality measurement
using for example a received signal strength indicator (RSSI). If
the signal quality measurement at the wireless unit (or at the base
station depending on the embodiment) is greater than the
macrodiversity trigger value, then the control system disables
macrodiversity, thereby disabling handoffs at block 70. Otherwise,
macrodiversity is enabled at block 72. Additionally, active set
threshold values for the wireless unit and/or a restricted or
limited set of candidate base stations, for example of certain
cells neighboring the home cell, can be established for the
wireless unit. With macrodiversity enabled, the wireless unit can
receive signals from the base stations on the active sets but will
not be handed off from the home base station. As such, handoffs are
disabled. The macrodiversity control system can accomplish this in
different ways, for example by preventing the wireless unit from
requesting handoffs, ignoring handoff requests and/or setting
handoff parameters.
[0039] Moreover, depending on the macrodiversity mode for the
wireless unit, the wireless system can enable/disable handoffs or
set the handoff parameters to different levels. For example, a
fixed wireless unit can have no handoff capability or no
macrodiversity capability; a limited fixed wireless unit can have
no or limited handoff capability or no, limited or full
macrodiversity capability; and a mobile wireless unit can have full
handoff capability and full macrodiversity capability. Depending on
the operating mode and/or parameters, such as signal quality
measurements, speed of mobile and/or traffic load of the cell 32
and/or surrounding cells, the macrodiversity and/or handoff
parameters defining the macrodiversity mode can be established on a
per wireless unit basis and/or on a call by call basis. For
example, a limited fixed wireless unit can have limited handoff
when the traffic load is light capability which is subsequently
switched to no or even more restrictive handoff capability when
load is heavier. Furthermore, in some embodiments, the registration
procedure is different for wireless units operating in different
modes. For example, where fixed (or limited fixed) wireless units
do not have handoff capability, registration procedures for those
wireless units can be eliminated.
[0040] In addition to the embodiment(s) described above, the
wireless communications system with a fixed mode according to the
principles of the present invention can be used with different
cellular systems and configurations which omit and/or add
components and/or use variations or portions of the described
system. For example, the macrodiversity control system is described
with particular reference to a cellular network architecture using
ANSI-STD-J-008, but other wireless systems using different multiple
access techniques, such as TDMA can be used and systems for sending
data and/or voice. It should be understood that different
notations, references and characterizations of the various
architecture blocks can be used. For example, the wireless system
using fixed, limited fixed and/or mobile modes has been described
using a particular wireless system, but it should be understood
that the system and portions thereof and of the described
architecture can be implemented in different locations, such as the
wireless unit, the base station and/or the MSC, or in application
specific integrated circuits, software-driven processing circuitry,
firmware or other arrangements of discrete components as would be
understood by one of ordinary skill in the art with the benefit of
this disclosure. What has been described is merely illustrative of
the application of the principles of the present invention. Those
skilled in the art will readily recognize that these and various
other modifications, arrangements and methods can be made to the
present invention without strictly following the exemplary
applications illustrated and described herein and without departing
from the spirit and scope of the present invention.
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