Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
1999-09-14
2002-09-10
Vo, Nguyen T. (Department: 2682)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S069000, C455S522000
Reexamination Certificate
active
06449489
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is generally related to a method and apparatus for improving a user's ability to gain access to a communication system and in particular to a method and apparatus for adjusting adaptively the power of a user equipment probing signal to increase the likelihood of detection by the communication system equipment.
2. Description of the Related Art
Communication systems, and in particular, wireless communication systems comprise a plurality of communication channels. through which subscribers of such systems communicate with each other and with the system. A portion of a typical wireless communication system is shown in FIG.
1
. The wireless communication system of
FIG. 1
depicts a cellular system comprising cells (e.g.,
102
,
104
,
106
,
108
) whereby each cell is a symbolic representation of the physical terrain or geographical region covered by communication network equipment commonly known as cell sites or base stations (e.g.,
110
,
112
,
114
).
Each base station has system equipment comprising radio equipment (i.e., transmitter, receiver, modulator, demodulator) that are used to transmit and/or receive communication signals between a base station and a user equipment. The system equipment can also be located at places other than base stations. The term “user” hereinafter is used interchangeably with the term “subscriber” to indicate an entity (i.e., person, facility or a combination thereof) who is allowed access (when possible) to the communication system. Access to the communication system is the ability of a subscriber to make use of the resources (e.g., system equipment, communication channels) of the communication system. The user equipment (e.g.,
140
in cell
104
) is typically a cellular phone or any other communication equipment that is used by a subscriber of a communication system. For example, the user equipment can be a wireless portable computer or a pager. The system equipment further comprises processing equipment for retrieving information being carried by the communication signals and for implementing procedures based on communication protocols.
A communication protocol is a set of procedures or processes that dictate how communications between users of the communication system is to be initiated, maintained and terminated. The communication protocol also dictates the communications between a user and system equipment. Communication protocols are part of well known and established standards that are followed by operators of communication systems.
Still referring to
FIG. 1
, each user communicates with a base station via a wireless communication link. For example in cell
104
, user
140
communicates with base station
114
via communication link
156
. Typically, each wireless communication link comprises several communication channels. For example, for a Code Division Multiple Access (CDMA) wireless system, the communication link comprises an Access channel, a Paging channel and a Traffic channel. The Access channel is a channel through which user equipment transmits protocol information to a base station. The protocol information is information used by the system equipment operate and/or control the communication system. For example, a user requesting access to the communication system is allowed to use the communication system after various protocol information have been exchanged between the base station and the user equipment. In allowing the user to have access to the communication system, the system equipment identifies the user as a subscriber of the system, finds resources (e.g., communication channels, base station equipment) that can be made available to the user and allows the user to use (transmit/receive information) such resources in accordance with the protocol being followed by the communication system.
The Paging channel is a channel through which system equipment (e.g., base station) broadcasts protocol information to users of the communication system. The traffic channel is the channel used by the users to communicate with each other or with the system. The information conveyed through the traffic channel is, for example, voice, data, video, facsimile information or any other information typically conveyed by users of communication systems. The traffic channel consists of two channels: the first channel is called the reverse link through which users transmit information which information is received by the base station (or other system equipment); the second channel is called the forward link through which the base station (or other system equipment) transmits lo information to a user. Each user has a forward link and a reverse link assigned by the communication system. In addition to the other channels discussed above, some CDMA systems also have a pilot channel that is used to assist a user to request and obtain access to the communication system.
The pilot channel is a channel through which the system equipment broadcast a pilot signal that covers a certain area (e.g., cell area) of the communication system. The pilot signal serves as a sort of beacon signal that advertises the existence of the base station for any user who wants access to the communication system. The pilot signal also serves as a timing signal for the user equipment; that is, a pilot signal received by a user equipment (e.g., cell phone) is one of several signals used by the user equipment to synchronize its timing to the timing of the base station. The pilot signal is typically a system defined carrier signal; that is, the pilot signal is typically a signal of a single frequency, f
c
. The user equipment has the proper hardware to receive and detect a pilot signal of appropriate power. Due to a well known phenomenon called the “Doppler effect,” the frequency of the pilot signal received by the user equipment is f
c
±f
d
where f
d
is called a “Doppler shift.” The Doppler shift is the change in the carrier frequency that occurs due to the relative motion of user equipment to the base station equipment (or other system equipment) from which the pilot signal is transmitted. When the user equipment is moving away from the base station, the Doppler shift is subtracted from the carrier frequency. When the user equipment is moving toward the base station, the Doppler shift is added to the carrier frequency. It is also well known that the speed of the user equipment relative to the base station equipment directly affects the value (i.e., the amount of shift) of the Doppler shift.
A user initiates a request for access to the communication system by transmitting a probe signal. The probe signal is typically also a signal of a certain frequency which is also affected by the Doppler effect. The probe has two portions: the first portion is called the preamble which is typically a string of “0” bits or a string of “1” bits. The second portion of the probe is a message portion containing protocol information. The preamble is the portion of the probe that allows the base station (or other system equipment) to detect the probe. The system equipment decodes the message portion of the probe. Once the probe preamble is detected and the probe message is decoded, the system equipment initiates a certain procedure (in accordance with a protocol being followed by the communication system) to provide access to the user that transmitted the probe signal. Prior to initiating the procedure, the system equipment transmits an “acknowledge” (ACK) message to the user equipment indicating to the user equipment that the probe signal has been detected. Once the user equipment receives the ACK message it no longer transmits the probe signal and proceeds as per the protocol to obtain access to the communication system.
In many cases the probe signal is not detected by the system equipment because the power (or amplitude) of the probe signal received by the system equipment is attenuated due to various effects of the communication link. In such cases, the user equipment transmits the probe signal repeat
Lu Ming
Zhu Pengfei
Lucent Technologies - Inc.
Narcisse Claude
Teitelbaum Ozer M. N.
Vo Nguyen T.
LandOfFree
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