System and methods for controlling access to digital...

Details System and methods for controlling access to digital... System and methods for controlling access to digital...

1998-12-21

2001-06-12

Nguyen, Lee (Department: 2683)

Telecommunications

Transmitter and receiver at same station

Radiotelephone equipment detail

C455S068000, C455S426100, C455S436000, C455S453000, C455S502000, C455S553100

Reexamination Certificate

active

06246886

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to wireless networks, more specifically to dual-mode wireless telephone communication networks that overlay digital cellular systems over existing analog-based cellular systems.
2. Background Art
Wireless telephone communication systems have evolved from the Advanced Mobile Phone Service (AMPS) technology, introduced around 1983, to more sophisticated digital-based air interface protocols. Specifically, the AMPS technology is an analog-based technology that uses frequency division multiple access techniques to divide the available radio spectrum into channel bandwidths, where each 30 kilohertz voice channel supports a single conversation.
FIG. 1
is a diagram illustrating a cellular communication system including an AMPS-based wireless telephone system
10
. As shown in
FIG. 1
, the AMPS system
10
includes an AMPS compliant base station
12
a
and a plurality of transceivers
14
configured for transmitting voice channels within the 800 MHz cellular band into overlapping propagation regions
16
, also referred to as cells. The arrangement of the antennas
14
at prescribed geographic locations establish a cellular-based coverage area
Digital access technologies have been developed based on Time Division Multiple Access (TDMA) or Code Division Multiple Access (CDMA) schemes. These digital access technologies are more efficient relative to analog-based access technologies such as AMPS. In TDMA, the RF carrier is divided into time slots. The digital system allocates speech to these time slots by converting and compressing speech information carried by analog voice signals into compressed digital samples using vocoding techniques, enabling the speech samples to fit into the time slots. Hence, 3 or more time slots may fit into each 30 kHz channel, resulting in at least a three-fold increase in capacity. The well-recognized TDMA-based GSM standard utilizes 8 time slots in 200 kHz bandwidth channels.
Code Division Multiple Access (CDMA) is an even more efficient access technology, where the compressed speech samples are spread over a large frequency band by coding each speech sample with a unique pseudorandom sequence. Multiple voice samples can then be sent through the same wide-frequency band. The digital wireless telephone having the correct pseudorandom sequence will reproduce the corresponding speech sample, whereas voice samples transmitted with different pseudorandom sequences will appear as background noise in the frequency band.
Hence, digital access technologies have substantial advantages over analog-based systems. Digital cellular systems, however, have not yet been deployed in as many regions as AMPS-based systems. Hence, digital cellular subscribers are offered continuous coverage using dual-mode wireless telephones capable of switching between a first mode (e.g., CDMA) and a second mode (e.g., AMPS) based on the availability of a certain technology.
As shown in
FIG. 1
, a dual-mode wireless communications system
20
includes an analog base station
12
b
of an analog wireless communications system, a digital cellular system (e.g., CDMA)
22
, and a plurality of antennas
24
configured for transmitting both wireless telephone signals from the AMPS base station
12
b
and the CDMA system
22
. Hence, the AMPS base station
12
b
transmits the analog cellular signals
26
into the appropriate cells
28
via the respective transceiver antennas
24
, establishing an analog-based wireless telephone system in the coverage areas
28
. Similarly, the CDMA system
22
establishes a digital wireless system by transmitting the CDMA-encoded signals
30
to the same antennas
24
(or separate co-located antennas), enabling the digital wireless system to overlie the prescribed coverage areas
28
of the analog-based system generated by the AMPS base station
12
b
. Hence, a dual-mode wireless telephone
32
is able to initiate and receive telephone calls within the cell sites
28
using the CDMA system
22
, and within the cell sites
16
using the AMPS system
12
a
AMPS wireless telephones (not shown) can initiate and receive telephone calls in the cell sites
28
using the AMPS system
12
b.
A problem encountered in the dual-mode system
20
occurs when the dual-mode wireless telephone moves across a boundary
34
between cellular systems
10
and
20
. In particular, assume the dual-mode telephone
32
is in active communication with the CDMA base station
22
for a call in progress while the subscriber moves across the border
34
from the cell sites
28
of the dual-mode system
20
to the cell sites
16
of the AMPS system
10
. As recognized in the art, the movement of the dual-mode wireless telephone
32
across the boundary
34
requires a hard handoff by the dual-mode telephone with the AMPS-based system
10
. The hard handoff from the CDMA-based system
22
within the dual-mode system
20
to the AMPS-based system
10
is one of the most complicated and signaling-intensive procedures in wireless networks, especially since the dual-mode wireless telephone
32
must switch from digital mode to analog mode simultaneously with the hard handoff. Hence the hard handoff from the CDMA system
22
to the AMPS system
10
has a substantial risk in dropping the call.
Although there is a desirability to minimize the risk in dropped calls, current dual-mode digital telephones
32
are configured for initially searching for the preferred digital technology, such as CDMA. Hence, the dual-mode wireless telephone
32
will connect with the alternative technology (e.g., AMPS) only if the dual-mode digital telephone
32
is unable to establish a link with the preferred digital (e.g., CDMA) technology. Hence, the dual-mode telephone
32
will always try to look for the preferred CDMA technology first. Consequently, the dual-mode telephone
32
cannot be controlled to avoid establishing a CDMA-based call while the digital telephone
32
is within the dual-mode cellular system
20
, even if there is a substantial probability that the dual-mode telephone
32
will move across the boundary
34
into the AMPS-based system
10
, risking a dropped call.
SUMMARY OF THE INVENTION
There is a need for an arrangement that minimizes the occurrence of dropped calls as a dual-mode telephone moves across a boundary from a dual-mode digital cellular system into an adjacent wireless telephone system having another wireless protocol.
There is also a need for an arrangement that enables a system to selectively overcome priority-based search techniques in dual-mode telephones configured for accessing a digital wireless telephone system prior to attempting access to alternative wireless telephone systems.
There is also a need for an arrangement enabling a dual-mode wireless telephone system having a digital wireless system to limit traffic in a selected propagation region and/or coverage area of the digital wireless system based on a detected traffic condition in the selected region or area.
These and other needs are obtained by the present invention, where a digital wireless communication system configured for transmitting digital wireless telephone signals into propagation regions selectively reduces transmission of a sync channel signal in a selected propagation region to a power level that is undetectable by digital telephones located within at least a selected portion of the selected propagation region. The transmission of the sync channel signal at the reduced power level undetectable by the digital telephone causes the dual-mode digital telephone, located within the selected portion of the selected propagation region, to search for alternative wireless telephone systems (e.g., AMPS-based analog systems), limiting access by the digital telephones. Hence, the digital wireless communication system can selectively limit access by the dual-mode digital telephones without transmitting any control signaling to the dual-mode digital telephones or requiring any modification to the dual-mode telephones.
According to one aspec

Affiliated with

Also associated with

Rating

System and methods for controlling access to digital... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with System and methods for controlling access to digital..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and System and methods for controlling access to digital... will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2490905