Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1998-12-21
2002-04-09
Vu, Huy D. (Department: 2661)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S342000, C370S318000, C370S401000, C455S422100, C455S560000, C455S522000
Reexamination Certificate
active
06370127
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to telecommunication networks, and more particularly, to a frame selection and power control CDMA architecture for telecommunication networks.
2. Discussion of the Related Art
In cellular telephone systems, a service area is divided into cells, each of which may be further divided into sectors. Each cell is serviced by a single base station (BS) and all of the base stations are connected to a mobile switching center (MSC) (also referred to as a Mobile Telephone eXchange (MTX)) via a base station controller (BSC) and hardware links (e.g., T1, E1, optical fiber, or satellite links). A plurality of mobile units (i.e., subscriber units) can be connected to the MSC by establishing radio links with one or more nearby base stations.
FIG. 1
illustrates an exemplary MSC and Code Division Multiple Access (CDMA) system architecture
10
. The MSC
12
is coupled to a Public Switched Telephone Network
14
(PSTN) or other public network. The CDMA system
10
includes a plurality of base station transceiver subsystems (BTSs)
16
, each of which define respective cells
18
. Each cell can have a coverage area radius on the order of approximately 1-6 miles, typical. Various components of mobile telephone systems are known in the art and thus only those components of mobile communications which are pertinent with respect to the present disclosure are disclosed and briefly described herein.
The system architecture of
FIG. 1
further includes abase station controller (BSC)
20
having a router
22
(also referred to as a CDMA Interconnect System (CIS)) and a selector
24
(SEL). The CDMA router
22
provides a packet routing function and allows the MSC-CDMA system
10
to be fully connected, i.e., any component can communicate with any other component in the system. The router
22
thus routes packets and provides any necessary communication between, for example, any base station transceiver subsystem (BTS)
16
, the selector (SEL)
24
, or the MSC
12
. The router is also capable of performing the broadcast of packets.
The selector (SEL)
24
handles an appropriate data formatting of voice data on the MSC-side and on the BTS-side of the selector. The SEL includes a selector subsystem including vocoder (voice coder/decoder) digital signal processors (DSPs) and call processing managements functions. The SEL
24
further receives control information from the MSC
12
via the router
22
. In particular, the selector (SEL) provides the functions of voice coding, multiplexing, handoff, power control, and radio link setup. A voice coding component provides conversion of pulse code modulation (PCM) format voice received from a digital trunk controller (DTC) of the MSC
12
into the CDMA format frames destined for the BTS
16
using a suitable coding technique. The digital trunk controller (DTC) supports trunk terminations to the PSTN
14
, furthermore, providing necessary processing and control functions between the MSC
12
and the PSTN
14
. The voice coding component also converts the CDMA format frames from the BTS
16
into the PCM format voice for use in the other direction. A multiplexing component processes all the IS
95
traffic frames to multiplex the voice, data and signaling information. The handoff component coordinates the communications between the subscriber unit
26
and multiple BTSs
16
. The power control component of SEL
24
maintains the mobile transmit power at a desired power level. Lastly, the radio link setup component of SEL
24
is used during call setup for preparing the traffic channel on the BTS.
In further discussion of the above, the selector (SEL) includes a plurality of independent DSP units. For each mobile station, there is a single DSP unit assigned. Only one DSP is used per call originating to/from a given subscriber unit or mobile station. The unique identifier of the subscriber unit determines which DSP of the plurality of DSPs the mobile station is dedicated to.
In the instance of a mobile station traveling from a first cell to a second cell, the selector (SEL) receives one packet plus a soft handoff packet, to be further discussed below. The selector (SEL) performs some prescribed call management, including power control, selecting the best input signal packet of the one or more packets received, and sending the selected packet to the corresponding DSP (i.e., a selector card of the SEL interfaces with a corresponding DSP).
The base station transceiver subsystem (BTS)
16
provides the radio link between subscriber units (also referred to as mobile stations/mobile units)
26
and the MSC
12
, wherein the BTS is located at a respective cell site. Located at the BTS or respective base station are the antennas, transmitter, receivers, power amplifiers, and interface hardware to support the link to the base station controller (BSC). Each base station provides a common air interface to the subscriber units according to the CDMA standard. For example, data from the subscriber unit
26
is converted to packets by the base station, and these packets plus additional control information are passed to the selector (SEL)
24
in the base station controller (BSC)
20
for further processing.
Each base station transceiver subsystem (BTS) thus corresponds to cell site equipment for the MSC-CDMA system and is used for performing various software functions. The BTS provides the IS
95
air interface between the MSC-CDMA system and the subscriber unit. In the forward direction, the BTS accepts packets from the SEL and modulates the information on the RF carrier and transmits the packet. In the reverse direction, the BTS demodulates the RF back into packets, adds additional control information and then routes the packets via the router to the SEL for further processing. The major functions provided by the BTS software include: Over-the-air RF interface with the subscriber unit; additional over-the-air functions such as pilot, sync, paging, and access channels; call processing functions to control the subscriber unit operation over the paging and access channels, including short message services; control and management of BTS resources; and monitoring and configuration functions. BTS can either be integrated to include both digital processing and RF components, or can be distributed to allow for remote location of the RF equipment from centralized digital equipment.
Communication between a mobile station (MS)
26
and the PSTN
14
is carried out from a respective BTS or BTSs
16
to the router
22
, from the router
22
to the selector (SEL)
24
, from the SEL
24
to the MSC
12
, and finally between the MSC
12
and the PSTN
14
. Each BTS communicates with the router via a T1 (or E1) link
28
. A T1 link is characterized by a communication rate of 1.54 megabits per second (Mbps) and an E1 link is characterized by a communication rate of 2 Mbps.
With the CDMA system
10
, a mobile station
26
can begin a call in a first cell and subsequently travel into a second cell. While the mobile station is in the first cell, communication will occur between the respective BTS and the router via a respective T1 link. During a transition between the first cell and the second cell, it is possible for more than one communication to occur for a given transmission, i.e., from more than one BTS and T1 link to the router. This situation occurs when a mobile station is talking to more than one BTS and in which a signal is transmitted from each BTS. In addition, the voice communication signal is a compressed voice signal, further being transmitted in the form of packets. The packets are sent through a respective T1 link from a respective BTS to the router for ultimate delivery to a dedicated DSP within the selector (SEL)
24
for the given call. Prior to reaching the corresponding DSP, the packet goes to the selector (SEL)
24
, wherein the selector
24
may receive multiple packets at any given time, each packet originating from a different BTS for a given call. The selector (SEL)
24
examines all p
Basu Kalyan
Daraiseh Abdel-Ghani
Landolsi Mohamed
Haynes and Boone LLP
Nortel Networks Limited
Phan Tri H.
Vu Huy D.
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