Reconfigurable wireless system base station

Details Reconfigurable wireless system base station Reconfigurable wireless system base station

1999-10-18

2003-07-01

Trost, William (Department: 2683)

Multiplex communications

Communication over free space

Having a plurality of contiguous regions served by...

C455S550100, C455S561000, C455S422100, C370S328000, C370S337000, C370S342000, C370S347000, C370S466000

Reexamination Certificate

active

06587448

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to base stations in code division multiple access (CDMA) wireless systems and other types of wireless communication systems, and more particularly to base stations capable of supporting multiple communication standards within such systems.
BACKGROUND OF THE INVENTION
The rapid pace of development in wireless communication systems has typically led to significant changes to the standards which define the operation of such systems. For example, the standards defining the operation of IS-95 CDMA wireless systems have progressed from TIA/EIA IS-95A to TIA/EIA IS-95B, and are now in the process of moving toward TIA/EIA IS-2000, also known as IS-95C. The IS-95A, IS-95B and IS-95C standards are collectively referred to herein as IS-95. Other CDMA standards, such as Multi-Carrier (MC) cdma2000 and the next-generation European standard known as Universal Mobile Telecommunication System (UMTS), are also being proposed.
These related standards each generally define an air interface specification that allows a mobile unit to communicate with a base station associated with a cell site. The interface definition typically includes a set of air interface channels, channel signal encoding rules, and signaling messages to enable the mobile unit to place and receive voice or data calls to and from a land line network, as well as to and from other mobile users. However, when the differences between successive generations of standards are significant, the base stations designed to support one standard often cannot easily be changed to support the next generation of the standard, thereby necessitating a new base station design. In many cases, this need for a new base station design arises because new air interface specifications require circuit packs in the base station to communicate different sets of signals than those communicated in accordance with a previous version of the standard. This situation will be illustrated in conjunction with
FIGS. 1 and 2
below.
FIG. 1
shows an example of a base station
100
configured in accordance with the above-noted. IS-95 standard. The base station
100
includes a control computer
102
, a control and traffic bus
104
, and a set of M channel unit boards
106
-i, i=1, 2, . . . M. The control computer
102
interfaces with a mobile switching center (MSC) which provides a link to other base stations and to a public switched telephone network (PSTN). In an IS-95 CDMA system, spread spectrum digital signals from different user calls on a given base station antenna sector are added together to generate a composite spread spectrum digital signal for that sector. Individual spread spectrum digital signals are generated by channel elements, such as cell site modems (CSMs), that are part of the channel unit boards
106
, and are combined to form the composite spread spectrum digital signal for a given sector. The base station design of
FIG. 1
allows the channel unit boards
106
to communicate signals from one such board to the next in support of users on one CDMA carrier, designated C
1
, and up to three 120° antenna sectors, designated &agr;,&bgr; and &ggr;. Three sector systems are commonly used in practice, although omni-directional and two-sector systems may also be deployed. The use of a larger number of sectors, such as six sectors, is less common, but also possible.
Within each channel unit board
106
-i in the base station
100
of
FIG. 1
, the spread spectrum digital signals of up to N users are added together on a per-sector basis. For each sector, the summed spread spectrum digital signals of users served by a particular channel unit board
106
-i are added to the respective signals from the previous channel unit board, i.e., the channel unit board to its left in the
FIG. 1
design. The summed digital signals are output from the channel unit board
106
-i, and become inputs to the next-in-line channel unit board
106
-(i+1) closer to a set of three radio boards
108
-
1
,
108
-
2
and
108
-
3
in FIG.
1
. Therefore, up to N users per channel unit board are added together by the mechanism of summing the signals from channel unit board to channel unit board. In a design with M such channel unit boards, each supporting up to N users, up to M×N total users can be supported on the three sectors &agr;,&bgr; and &ggr;. The interconnections between the channel unit boards are provided by a transmit digital'signal communications bus denoted Tx-bus.
It should be noted that although the description herein will be directed primarily to the transmit operations of the base stations, similar interconnection issues arise with respect to receive operations. The corresponding receive bus (Rx-bus) is omitted from FIG.
1
and other similar base station illustrations herein for purposes of clarity.
The digital processing elements on each of the channel unit boards
106
-i can be used to support a user call on any of the three sectors &agr;, &bgr; and &ggr;. This capability is referred to as channel element pooling, and in the
FIG. 1
design, is applied to one carrier and three sectors. Digital in-phase (I) and quadrature phase (Q) signals, for each of the three sectors &agr;,&bgr; and &ggr; and the one CDMA carrier C
1
are summed from channel unit board to channel unit board, and finally are passed to one of the three radio boards
108
-
1
,
108
-
2
and
108
-
3
, depending on the sector. Each radio board
108
-
1
,
108
-
2
and
1
,
08
-
3
converts the digital I and Q signal inputs into an RF signal. The RF signals for sectors &agr;, &bgr; and &ggr; are then amplified by power amplifiers
110
-
1
,
110
-
2
and
110
-
3
, filtered in transmit filters
121
-
1
,
112
-
2
and
112
-
3
, and radiated by transmit antennas
114
-
1
,
114
-
2
and
114
-
3
, respectively. Other types of conventional techniques may be used to communicate signals among the channel unit boards, e.g., the I and Q signals for each sect or may be multiplexed onto one back plane trace.
A basic problem with conventional base station designs such as that shown in
FIG. 1
is the configuration of the transmit digital signal communications bus (Tx-bus) that interconnects the channel units boards
106
. More particularly, it is generally very difficult to be able to redefine the bus according to the particular version of the standard that is being implemented, and according to the set or subset of features that are to be provided in a specific configuration of a given base station. The Tx-bus also needs to be able to support the radio boards used in the base station, and these radio boards likewise need to be capable of interpreting the, communications bus signals in different ways, depending on configuration commands they receive from a control program. Although the digital processing boards and the radio boards may be hard wired for specific bus signal usage,several board design types would then be required to cover all versions of the standards.
FIG. 2
illustrates the manner in, which the
FIG. 1
base station design can be extended to support an additional CDMA carrier C
2
. Since the IS-95A RF signal occupies a bandwidth of 1.25 MHz, it is possible and desirable for base stations to support multiple CDMA carriers. However, the base station design of
FIG. 1
generally cannot simply incorporate additional channel unit boards
106
in a direct way to provide service on the second CDMA carrier C
2
. Instead, the board interconnect structure of
FIG. 1
needs to be completely replicated, in the manner show in
FIG. 2
, in order to provides service on the second carrier C
2
. The
FIG. 2
base station
100
′ therefore includes an additional set Of channel unit boards
116
-
1
, . . .
116
-M. The base station
100
′ also includes an additional set of radio boards
118
-
1
,
118
-
2
and
118
-
3
, power amplifiers
120
-
1
,
120
-
2
and
120
-
3
, and filters
122
-
1
,
122
-
2
and
122
-
3
, for processing signals associated with sectors &agr;, &bgr; and &ggr;, respectively, and carri

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