Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1999-11-24
2003-11-25
Vo, Nguyen T. (Department: 2681)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C455S437000, C455S440000
Reexamination Certificate
active
06654362
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to wireless communication systems and, in particular, to handoff in wireless communication systems.
2. Description of the Related Art
The operation of wireless communication systems is in large part defined by industry standards. These standards specify the air interface specification that allows a mobile terminal to communicate with a base station. The air interface specification typically includes a set of air interface channels, channel signal encoding rules, and signaling messages to allow the mobile terminal to communicate with the base station. The standards include standards for Advanced Mobile Phone Service (AMPS), Time Division Multiple Access (TDMA), Code Division Multiple Access (CDMA), Global System for Mobile (GSM) technologies. The rapid pace of development in wireless communication systems has typically led to multiple standards within some of the technologies, such as CDMA. For example, some of the standards in CDMA technology include IS-95, CDMA 2000, wideband CDMA, and Universal Mobile Telecommunication System (UMTS).
A particular wireless communication system will comply with one, or possibly several, standards. For example, many wireless communication systems that comply with either one of the CDMA standards or one of the TDMA standards are designed to also comply with the AMPS standards. Systems that comply with more than one standard maximize geographic coverage for users since these systems allow a user who is capable of using either standard to use the wireless communication system.
A wireless communication system usually serves a specific limited geographic area and operates over a particular frequency band. The frequency band is assigned by the FCC for a particular geographic area. The geographic area served by one wireless communication system will typically border on, or overlap, with the geographic area served by another wireless communication system. In the case of adjacent wireless communication systems, the systems may operate either over the same or over different frequency bands, and may comply with either the same or with different standards. In the case of two overlapping wireless communication systems, the systems will operate over different frequency bands, and may comply with the either the same or with different standards.
FIG. 1
illustrates two wireless communication systems, wireless communication system
100
, and wireless communication system
200
. The geographic areas serviced by wireless communication systems
100
and
200
are divided into a plurality of spatially distinct areas called “cells,”
102
and
104
, and
202
, respectively. Although cells
102
,
104
, and
202
are illustrated as a hexagon in a honeycomb pattern, each cell is actually of an irregular shape that depends on the topography of the terrain surrounding the cell. Although there are only two cell shown for wireless communication system
100
and one cell shown for wireless communication system
200
, one skilled in the art will appreciate that each wireless communication system typically has a much larger number of cells. Each cell
102
,
104
,
202
contains one base station
112
,
114
, and
212
, respectively. Base stations
112
and
114
include equipment to communicate with Mobile Switching Center (“MSC”)
120
, which is connected to local and/or long-distance transmission network
122
, such as a public switch telephone network (PSTN). Base station
212
includes equipment to communicate with Mobile Switching Center (“MSC”)
220
, which is connected to local and/or long-distance transmission network
222
, such as a public switch telephone network (PSTN). Each base station
112
,
114
, and
212
also includes antennas and radios, which include a receiver and transmitter. The base stations use the antennas and radios to communicate with mobile terminals
124
,
126
.
When a call is set up in wireless communication system
100
, mobile terminal
124
communicates with the base station from which mobile terminal
124
receives the strongest signal, in this case base station
112
. As mobile terminal
124
moves from one cell to another, continuous service is provided by “handing off” mobile terminal
124
from the base station in cell where the mobile terminal is located to the base station in the cell into which the mobile terminal is moving. Based on measurements of signals sent to and received from mobile terminal
124
, base station
112
determines the best base station with which it can participate in a handoff of mobile terminal
124
, referred to herein as a handoff candidate. The receiver and transmitter of the handoff candidate are referred to herein as the candidate receiver and the candidate transmitter, respectively. In CDMA systems, base station
112
starts the process of searching for a handoff candidate when the signal received by mobile terminal
124
from base station
112
falls below a certain threshold. The mobile terminal is continuously measuring the pilot signals from base stations in adjacent cells. Base station
112
then analyzes these signal measurements to determine the handoff candidate. In AMPS and in some TDMA systems, base station
112
starts the process of searching for a handoff candidate when the signal received by the base station from the mobile terminal falls below a certain threshold. Base station
112
searches for a handoff candidate by analyzing the signals from base stations in adjacent cells. The base station requests the base stations in adjacent cells to measure the signals received by them from mobile terminal
124
. Base station
112
then analyzes these signals to determine the handoff candidate. In TDMA systems that have mobile assisted handoff, both the signal received by the base station from the mobile terminal and the signal received by the mobile terminal to the base station is used to determine when the base station starts the process of searching for a handoff candidate.
A problem occurs when mobile terminal
124
may need to be handed off between two wireless communication systems. For example, when base station
112
is in a cell on the edge of wireless communication system
100
, such as cell
102
, and wireless communication system
200
either does not operate over the same frequency band, and/or does not comply with the same standard as wireless communication system
100
. This is a problem because before mobile terminal
124
can be handed off, the mobile terminal needs to communicate with a base station in wireless communication system
200
and determine the characteristics and environment in wireless communication system
200
. In order to communicate with a base station in wireless system
200
, mobile terminal
124
needs to switch to operate in the same frequency band as communication system
200
. Mobile terminal
124
also needs to switch to comply with the standard with which wireless communication system
200
complies. The mobile terminal then needs to communicate with base station
212
. Since mobile terminal
124
is not aware of the characteristics of base station
212
, it takes mobile terminal
124
a significant amount of time to establish communication with base station
212
. For, example, when both wireless communication systems
100
and
200
comply with a CDMA standard, mobile terminal
124
needs to: switch to the appropriate frequency for wireless communication system
200
; locate and synch to the pilot signal from base station
212
; and register with and be authenticated by wireless communication system
200
. During this time, mobile terminal
124
cannot communicate with base station
112
because base station
112
operates in a different frequency band and/or complies with a different standard. The significant amount of time required to perform the handoff may result in the call being dropped, or in the user of mobile terminal
124
hearing noise or silence, which is a disruption of the call and an inconvenience to the user.
Accordingly, there exists a need f
Legree Tracy M.
Lucent Technologies - Inc.
Vo Nguyen T.
LandOfFree
Use of location in handoff in wireless communication systems does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Use of location in handoff in wireless communication systems, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Use of location in handoff in wireless communication systems will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3184622