Methods, systems and devices for cascaded communications

Details Methods, systems and devices for cascaded communications Methods, systems and devices for cascaded communications

2000-03-03

2003-09-16

Urban, Edward F. (Department: 2685)

Telecommunications

Carrier wave repeater or relay system

Monitoring

C455S423000, C455S424000, C455S422100, C370S349000, C370S238000

Reexamination Certificate

active

06622005

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to communications systems and methods, and more particularly, to communications systems including devices, such as wireless radio heads, base stations or other transceiver apparatus, connected in cascade by respective communications links, such as T1 links.
Wireless communications systems are commonly employed to provide voice and data communications to subscribers. For example, analog cellular wireless communications systems, such as those designated AMPS (Advanced Mobile Phone System), NMT(Nordic Mobile Telephone)-450 and NMT-900, have long been deployed successfully throughout the world. Digital cellular wireless communications systems such as those conforming to the North American standard IS-54 and the European standard GSM (Global Systems for Mobile Communications) have been in service since the early 1990's. More recently, a wide variety of wireless digital services broadly labeled as PCS (Personal Communications Services) have been introduced, including advanced digital cellular systems conforming to standards such as TIA/EIA-136 and IS-95, lower-power systems such as DECT (Digital Enhanced Cordless Telephone) and data communications services such as CDPD (Cellular Digital Packet Data). These and other systems are described in
The Mobile Communications Handbook
, edited by Gibson and published by CRC Press (1996).
FIG. 1
illustrates a typical terrestrial cellular wireless communication system
20
. The cellular wireless communications system
20
may include one or more terminals
22
, such as mobile terminals, radiotelephones or similar devices, communicating with a plurality of cells
24
served by base stations
26
and a mobile telephone switching office (MTSO)
28
. Although only three cells
24
are shown in
FIG. 1
, a typical cellular system may include hundreds of cells, may include more than one MTSO, and may serve thousands of terminals.
The cells
24
generally serve as nodes in the communication system
20
, from which links are established between terminals
22
and the MTSO
28
, by way of the base stations
26
serving the cells
24
. Each cell
24
typically has allocated to it one or more dedicated control channels and one or more traffic channels. A control channel is a dedicated channel used for transmitting cell identification and paging information. The traffic channels carry the voice and data information. Through the cellular system
20
, a duplex radio communication link may be effected between two mobile terminals
22
or between a mobile terminal
22
and a landline telephone user
32
through a public switched telephone network (PSTN)
34
. The function of the base station
26
is to handle radio communication between a cell
24
and mobile terminals
22
. In this capacity, the base station
26
functions as a relay station for data and voice signals.
As illustrated in
FIG. 2
, a conventional indoor wireless network
200
that communicates with one or more mobile terminals
22
′ includes one or more radio heads
210
, a Control Part (COP)
220
(sometimes referred to as a Control and Radio Interface;(CRI) or Radio Control Interface (RCI)), and a mobile switching center (MSC)
230
. The radio heads
210
may include one or more radio transceivers and are typically distributed around a building or corporate campus, and provide air interface (radio coverage) functions for cells
240
in under control of the COP
220
in a manner similar to the base stations
26
illustrated in FIG.
1
. The air interface implemented by the radio heads
210
and COP
220
may take many forms, including, but not limited to, time division multiple access (TDMA) (e.g., per GSM, IS-136 or similar standards), code division multiple access (CDMA) (e.g., per IS-95, CDMA2000, or similar standards), and more traditional frequency division multiple access (FDMA). Although
FIG. 2
illustrates two cells
240
served by the respective radio heads
210
, a typical indoor wireless network may have several cells, and each cell may be serviced by one or more radio heads.
The radio heads
210
are connected to the COP
220
by communications links
215
over which data (e.g., frames for wireless communications) and control information are conveyed. In an exemplary RBS 884 Pico Cellular Base Station produced by Ericsson, Inc., the assignee of the present application, the links
215
are T1 (also referred to as DS-1) links which convey messages using a proprietary protocol which includes elements of the Link Access Protocol D (LAPD) Layer
2
protocol used on channels under the Integrated Digital Services Network (ISDN) suite of protocols.
As is well known to those skilled in the art, ISDN provides services that offer “B” channels that typically carry user data, and “D” channels that typically carry control and signaling information (with some user data transmission under certain circumstances). ISDN Basic Rate Interface (BRI) includes two B channels and one D channel, and its physical layer is specified in ITU-T I.430. ISDN Primary Rate Interface (PRI), typically transmitted over T1 links, includes
23
B channels and one channel in North America, and its physical layer is specified in ITU-T I.431. The channel signaling protocol includes Layers
1
-
3
, which follow the Open System Interconnect (OSI) model. The Physical Layer (Layer
1
) protocol is specified in ITU-T I.431. The Data Link Layer (Layer
2
) protocol is referred to as LAPD, as specified in the Q.921 Recommendations. The Network Layer (Layer
3
) protocol is specified in the ITU Q.931 Recommendations.
On a typical T1 link such as one the links
215
of the indoor wireless system
200
of
FIG. 2
, information is typically transmitted at 1544 kilobits per second (kb/s), in 193 bit Layer
2
frames that occur every 125 microseconds (&mgr;sec). A frame includes a 192-bit payload preceded by a framing (F) bit. An Extended SuperFrame (ESF) includes 24 consecutive frames, with the F bits being used to provide framing functions, a block error check (CRC) channel and a data link (DL). The ESF DL may be used for transmission of scheduled (periodic) maintenance messages and unscheduled priority and control codewords related to maintenance of transmission quality on the T1 link.
A structure for a Performance Report Message (PRM) transmitted on an ESF DL is provided in Table 1. A PRM includes a 13-byte information block bracketed by opening and closing flag bytes. The information bytes, including a header and a footer, are structured as an Unnumbered Information frame according to the LAPD protocol. The data content (body) of the frame is a concatenation of four 2-byte. representations of signal performance for respective one second periods. Each PRM typically includes data for the four most recent seconds, which can provide redundancy if the PRM is corrupted in transmission. A PRM is typically transmitted once every second, and is transmitted in 30 milliseconds (msec).
TABLE 1
PRM Format
The fields of the PRM may be described as follows:
FLAG:
Bytes 1 and 15 are the same as the DL idle code
(01111110) and serve to separate the PRM from other
signals that can appear on the DL.
SAPI:
(Service Access Point Identifier) Bits 3-8 identify the
information package as a PRM.
C/R:
(Command/Response) Bit 2 in the second byte identifies the
source of the PRM. If this bit is set to 1, the PRM was
generated from the carrier (central unit)
end of the T1 link; if this bit is 0, the PRM was generated
from the customer end of the T1 link.
EA:
(Extended Address) Bit 1 in bytes 3 and 3 are set
to 0 and 1, respectively.
TEI:
(Terminal Endpoint Identifier) May be used to identify
a device, as discussed in greater detail below.
CONTROL:
Byte 4 is set to 00000011 to indicate an
unacknowledged frame.
FCS:
(Frame Check Sequence) Byte 13 and 14 form a 16-bit
Cyclic Redundancy Check (CRC) code word that is
calculated on bytes 2-12.
G1-G6:
(CRC error events) These 6 bits are used to report CRC
error events that have occurred in the reported second.
SE:
(Severely Errored framing event

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