Multiplex communications – Communication over free space – Combining or distributing information via code word channels...
Reexamination Certificate
1999-06-11
2003-10-07
Maung, Nay (Department: 2681)
Multiplex communications
Communication over free space
Combining or distributing information via code word channels...
C370S332000
Reexamination Certificate
active
06631126
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to telecommunications, and, in particular, to wireless communications systems conforming to a code-division, multiple-access (CDMA) standard, such as the cdma2000 standard of the IS-95 family of CDMA wireless standards.
2. Description of the Related Art
FIG. 1
shows a block diagram of a conventional CDMA wireless communications system
100
. Communications system
100
is assumed to conform to the cdma2000 standard in the IS-95 family of CDMA wireless standards, although the present invention is not necessarily so limited. Communications system
100
comprises an interworking function (IWF)
102
connected to a radio link protocol (RLP) function
104
, which is in turn connected to a frame selection/distribution (FSD) function
106
, which is in turn connected to one or more base stations
110
via back haul facilities
108
(e.g., T1 lines). Depending on the specific implementation, IWF function
102
, RLP function
104
, and FSD function
106
may be, but need not be, physically separate functions.
Each base station
110
is capable of simultaneously supporting wireless communications with one or more mobile units
112
. FSD function
106
performs a forward-link frame distribution function in which frames of data corresponding to user messages are distributed to the various base stations. In addition, FSD function
106
performs a reverse-link frame selection function in which frames of data received from the various base stations are processed for forwarding on to RLP function
104
. In the forward-link direction, RLP function
104
segments user messages received from IWF function
102
into frames of data for distribution by FSD function
106
. In the reverse-link direction, RLP function
104
reassembles packets of data received from FSD function
106
into user messages for forwarding on to IWF function
102
. IWF function
102
implements a high-level point-to-point protocol (PPP) to perform certain centralized functions for communications system
100
to coordinate and control operations at the various base stations
110
. IWF function
102
also functions as the interface between communications system
100
and other communications systems (not shown) to provide a full range of telecommunications services to the mobile units, including voice communications with a remote end unit and/or data communications with a computer server or other nodes of a computer network.
As used in this specification, the term “mobile unit” as well as its synonyms “mobile user,” “mobile,” and “user,” will all be understood to refer to any end node communicating via wireless transmissions with one or more base stations of a wireless communications system, whether that end node is actually mobile or stationary. Also, as used in this specification, the term “base station” is synonymous with the terms “call leg” (or “leg” for short) and “cell site” (or “cell” for short).
The cdma2000 standard supports different modes of data communications. For relatively low rates of data messaging, a fundamental channel (FCH) can handle both signaling and data messaging. Signaling refers to the communications between a mobile and a base station that are used by the mobile and the base station to control the communications links between them, while messaging refers to the information passed through the base station to and from the end nodes of those communications, where the mobile is one of those end nodes. For high-rate data messaging, a supplemental channel (SCH) can be used for data messaging, while the fundamental channel handles the signaling between the mobile and the base station. Alternatively, when an SCH is used for data messaging, the signaling between the mobile and the base station can be handled by a special communications channel called a dedicated control channel (DCCH), which requires less power to transmit than an FCH, which is designed to handle low-rate data messaging in addition to signaling.
FIG. 2
shows a functional block diagram of a portion of communications system
100
of
FIG. 1
for a mobile unit
112
operating in soft handoff with three base stations
110
. Soft handoff refers to a situation in which a mobile unit is simultaneously communicating with two or more base stations, each of which is referred to as a call leg of those communications. Frame selection/distribution function
106
supports the soft handoff communications between mobile unit
112
and the three base stations
110
.
During normal voice communications, mobile
112
transmits voice messages using a reverse-link fundamental channel. Each of the three base stations
110
in soft handoff with mobile
112
receives the reverse-link FCH, accumulates voice messages into reverse-link packets, and transmits the reverse-link packets over back haul
108
to FSD function
106
. FSD function
106
receives the reverse-link packets from all three base stations, identifies sets of corresponding reverse-link packets (one reverse-link packet from each base station corresponding to the same voice messages received from the mobile), and selects one reverse-link packet from each set of corresponding reverse-link packets to transmit to the rest of the wireless system for eventual transmission to the remote end of the call (e.g., a connection with a regular PSTN user or possibly another mobile unit in communications system
100
).
At the same time, FSD function
106
receives forward-link packets containing voice messages from the remote end of the call intended for mobile unit
112
. FSD function
106
distributes copies of each forward-link packet to all of the base stations currently in soft handoff with the mobile. Each base station transmits the forward-link packets to mobile unit
112
using a different forward-link fundamental channel. Mobile unit
112
receives all three forward-link FCHs and combines corresponding voice messages from all three forward-link FCHs to generate the audio for the person using mobile unit
112
.
The timing of the distribution of the copies of the forward-link packets from FSD function
106
to the three base stations is critical, because mobile unit
112
needs to receive each set of corresponding voice messages from all three forward-link signals within a relatively short period of time in order to be able to combine all of the corresponding voice messages together. Similarly, FSD function
106
needs to receive all of the corresponding reverse-link packets from the different base stations within a relatively short period of time in order to coordinate the selection of packets for further processing. In order to satisfy these forward-link and reverse-link timing requirements, whenever a new call leg is added at a base station (i.e., whenever a new base station begins communications with a particular mobile unit in soft handoff), special synchronization procedures are performed between the base station and FSD function
106
, e.g., in order to ensure proper synchronization of that base station's forward-link transmissions with the forward-link transmissions from the other base stations currently participating in soft handoff with the mobile. These synchronization procedures involve specific communications back and forth between the base station and the FSD function over the back haul.
Although a fundamental channel can support some modest amount of data messaging in addition to voice messaging, the cdma2000 standard also supports high-speed data messaging via supplemental channels. According to the cdma2000 standard, since data messaging is typically bursty (i.e., intermittent), as opposed to the continuousness of voice messaging, supplemental channels are established and maintained only for the duration of each data burst. During a burst of data messaging via an assigned SCH, the mobile unit is said to be in an active state. Between bursts of data messaging when no SCH is currently assigned, but when an FCH (or DCCH) is assigned, the mobile unit is said to be in the control hold state.
Analogous to the
Berliner Edward F.
Rubin Harvey
Lucent Technologies - Inc.
Maung Nay
LandOfFree
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