Base station for mobile radio telecommunications systems

A base station (10) for mobile radio telecommunications systems comprises a radio frame set (11), an amplifier frame (12) and an antenna interface frame (13) connected to transmit and receive antennas (22 and 23). The radio frame set (11) comprises a radio channel frame (14) including a radio control complex (31), a plurality of radio channel units (54) and a plurality of digital interface circuits (57) for interconnecting the base station to a remote mobile telephone switching office. A time division multiplexed bus (53), connected to the radio control complex (31), the radio channel units (54) and the interface circuits (57), is used for selectively connecting, under the control of the radio control complex (31), any radio channel unit (54) to any digital interface circuit (57). Such a radio channel arrangement is capable of handling analog, as well as, digital radio channel units while exhibiting greater capacity, easier maintenance and upgrade, and substantially increased flexibility (FIG. 3).

TECHNICAL FIELD 
The present invention relates to mobile radio telecommunications systems 
and, more particularly, to an improved base station for use in cellular 
telecommunications systems. 
BACKGROUND OF THE INVENTION 
In high capacity cellular mobile radiotelephone systems, a plurality of 
base stations, also referred to as cell sites, are arranged so that each 
cell site covers a respective geographical area called a cell. Typically, 
each such cell site contains a radio transmitter-receiver and is directly 
wired to a mobile telephone switching office (MTSO) which in turn is part 
of a regional or nationwide network of telephone switching offices. One 
example of such cell site is the AT&T Series I cell sites (Model 1 and 
Model 2 architecture) used in the family of AUTOPLEX.RTM. cellular 
telecommunications systems which are commercially available from the 
American Telephone and Telegraph Company of New York, N.Y. Such known cell 
sites have operated satisfactorily for their intended purposes for which 
they were originally designed. However, because of increased demands for 
more radio channels occupying smaller physical facilities in combination 
with requirements of integrating digital data links and facilities in the 
radio frames at the site, there exists a need for a digital cell site 
capable of handling analog as well as digital radio channel units while 
exhibiting greater capacity, easier maintenance and upgrade, and more 
flexibility than now exist with commercially available equipments. 
SUMMARY OF THE INVENTION 
The foregoing need is met in an embodiment of the invention wherein a base 
station for mobile radio telecommunications systems comprises a radio 
channel frame including a radio control complex and a plurality of radio 
channel units located within the frame; communication links for 
bidirectionally coupling the base station to a remote mobile 
telecommunications switching office; a plurality of digital interface 
circuits, located within the radio channel frame, for interconnecting the 
radio channel frame to the communication links; and multiplexing bus 
arrangement connected between the radio control complex and the radio 
channel units for selectively connecting, under the control of the radio 
control complex, any one of the plurality of radio channel units to any 
one of the plurality of digital interface circuits. 
In accordance with another embodiment, a radio channel frame for cellular 
telecommunications systems comprises a control processing unit; a system 
bus coupled to the control processing unit; a memory circuit, a network 
control interface circuit and a communications processor interface circuit 
each connected to the system bus so that the control processing unit is 
capable of accessing each of the circuits; a plurality of radio channel 
units, each capable of performing setup, locate and voice channel 
functions; a plurality of digital interface circuits for interconnecting 
the radio channel frame to incoming and outgoing voice and data frame 
links; and multiplexing bus arrangement adapted for selectively coupling 
under the control of the control processing unit any one of the plurality 
of radio channel units to any one of the plurality of digital interface 
circuits. 
In accordance with a preferred embodiment, a radio channel frame for 
cellular telecommunications systems comprises first and second control 
processing units adapted to be interconnected by an update bus; first and 
second system buses respectively coupled to the first and second control 
processing units; first and second memory circuits respectively connected 
to the first and the second system bus so that each control processing 
unit is capable of accessing the first and second memory circuits; first 
and second network control interface circuits respectively connected to 
the first and the second system bus; first and second communications 
processor interface circuits respectively connected to the first and the 
second system bus; a plurality of radio channel units each capable of 
performing setup, locate or voice channel functions; a plurality of 
digital interface circuits for interconnecting the radio channel frame to 
incoming and outgoing voice and data frame links; and time division 
multiplexed bus arrangement adapted for selectively coupling, under the 
control of either one of the control processing units, any one of the 
plurality of radio channel units to any one of the plurality of digital 
interface circuits.

DETAILED DESCRIPTION 
Shown in FIG. 1 is a schematic representation of cell site 10 which 
illustratively includes three different frames, namely a radio frame set 
11, an amplifier frame 12 and an antenna interface frame 13. Included 
within the radio frame set 11 is at least one radio channel frame 14, 
called the primary frame. Additional radio channel growth frames, such as 
frames 15 and 16, may be selectively added to the primary radio channel 
frame 14 depending upon the capacity desired at the cell site 10. 
Similarly, an additional amplifier frame and a second antenna interface 
frame may be added to the cell site 10 based upon the overall requirements 
and capacity of the cell site 10. Also shown in FIG. 1 is a mobile 
telephone switching office (MTSO) 17 which is adapted to link a cellular 
or mobile subscriber (not shown) into the standard telephone network as 
well to other cellular subscribers. All data and voice communications 
between the MTSO 17 and the cell site 10 are achieved, respectively, over 
data links 18 and voice trunks 19 connected between the radio frame, such 
as primary radio channel frame 14, and the MTSO 17. Although links 18 and 
trunks 19 are each illustratively shown as a single connecting line, each 
such link or trunk consists of a plurality of physical connections between 
the MTSO 17 and the primary radio channel frame 14, for example. 
Radio signals to be transmitted from the MTSO 17 via the cell site 10 to a 
cellular subscriber, i.e., radio transmissions in the forward direction, 
are derived from the radio frame set 11 and coupled, via lead 20, to the 
amplifier frame 12 for appropriate amplification prior to transmission. 
The amplified signals to be transmitted are then connected, via lead 21, 
to the antenna interface frame 13 for radio transmission via a 
transmitting antenna 22. Radio transmission in the reverse direction, 
i.e., signals received at the cell site 10 from cellular subscribers, are 
received at the receiving antennas 23, and coupled to the radio frame set 
11 via the antenna interface frame 13 and lead 24. 
In accordance with an illustrative embodiment of the invention, the primary 
radio channel frame 14, shown in FIG. 2, includes an interconnection panel 
30, a radio control complex 31, a plurality of radio channel units 32 
arranged in several shelves within the frame, with each shelf comprising 
associated power supplies, power combiners/dividers, switches, and digital 
signaling format, e.g., DS1, interfaces. Also included in the radio 
channel frame 14 is a radio test unit 33 used primarily to check the 
performance of the total RF path to and from the receive and transmit 
antennas 23 and 22. 
Referring now to FIG. 3 which shows an overall functional block diagram of 
the primary radio channel frame 14, the radio control complex 31 is 
illustratively shown as having two interconnected identical sides, 
referred to as side 0 and side 1. However, as it will become clear from 
the following description, only one side is necessary for the operation of 
the radio control complex 31. Clearly, a duplex configuration of the radio 
control complex 31 substantially enhances reliability of the cell site 
through duplication, in that while one side is active, its mating side is 
kept in a dormant state but ready to take control with a minimum loss of 
information in the event of failure of the active side. The radio control 
complex 31 includes two identical processors 40 and 41 interconnected by 
an update bus 42. Each processor provides the control processing function 
for the radio control complex 31. Normally, one processor, e.g., 40, is 
active and the other processor, i.e., 41, is in a standby mode. On side 0 
of the radio control complex 31, the processor 40 is connected to a system 
bus 43 which in turn is coupled to a memory circuit 44, a communication 
processor interface circuit 45, at least one network control interface 46, 
and an alarm interface 47. Similarly, on the side 1 of the radio control 
complex 31, the processor 41 is connected to a system bus 48 which in turn 
is coupled to a memory circuit 49, a communication processor interface 
circuit 50, at least one network control interface 51 and an alarm 
interface 52. 
The update bus 42 lets the active, call processing, processor, e.g., 40, 
keep its mate's memory 49 updated to allow the processors to switch roles, 
i.e., responsibility for call processing, without losing valuable 
information. Also, the update bus 42 allows the active processor, e.g., 
40, to perform diagnostics on the mate processor, i.e., processor 41. 
Alternatively, if processor 41 is the active one, then the update bus 42 
allows the updating of memory 44 so that processor 40 can take over the 
control of the call processing in case of failure of processor 41. 
In accordance with an illustrative embodiment of the invention, the primary 
radio control frame 14 further includes at least one time division 
multiplexed bus 53 adapted to selectively connect, under control of either 
processors 40 or 41, a corresponding side of the radio control complex 31 
to additional circuits within the frame 14. Such additional circuits 
include several radio channel units, of which only one is shown as RCU 54, 
clock and tone circuits 55 and 56, several digital facility interface 
circuits of which only one is shown in FIG. 3 as DSI 57, and at least one 
radio test unit 58. In accordance with a preferred embodiment, the 
processors 40 and 41 include known commercially available processing 
units, such as MC68020 microprocessors and support logic including timers, 
registers, memory (read only memory and random access memory) and update 
bus control circuitry. The memory circuits 44 and 49 may each, for 
example, contain a 36 bit one megabit DRAM of known type with associated 
control, refresh, timing and write protect logic necessary to access it. 
The communication processor interface circuits 45 and 50 are adapted to 
provide reliable control channels with the MTSO 17 through the time 
division multiplexed bus 53 and the digital interface facility 57. 
Synchronization of control channel messages between the processors 40 and 
41 and the time division multiplexed bus 53 is provided by the network 
control interface circuits 46 and 51 respectively associated with side 0 
and side 1 of the radio control complex 31. 
As shown in FIG. 3, the time division multiplexed bus 53 preferably employs 
a pair of buses designated "A" and "B" to connect all the radio channel 
units, such as RCU 54, within the primary radio channel frame 14 and 
selected radio channel units in any optional growth radio channel frames, 
e.g., 15 or 16, in the event that such growth frames are used. In such 
case, an additional time division multiplexed bus is needed to 
interconnect the additional RCUs in the growth frames. All external 
interfaces, i.e., voice trunks 19 and data links 18 to and from MTSO 17, 
are connected to the time division multiplexed bus 53 via digital facility 
interfaces such as interface 57. All data links 18 from the MTSO 17 are 
connected to the bus 53 in the primary frame even through additional 
growth radio channel frames, such as 15 and 16, may be utilized. In 
accordance with a preferred embodiment, the bus 53 comprises a pair of 
8-bit time division multiplexed buses "A" and "B" to permit voice, data, 
and control connectivity to any circuit connected to the bus 53. 
Illustratively, each bus "A" and "B" may support 256 time slots and 
operates at a clock frequency of 2.048 MHz. Separating the bandwidth into 
two physically separate buses "A" and "B" has two advantages. First, it 
cuts in half the frequency at which a single 512 time slot bus must 
operate at, and second it provides increased system reliability. If one 
bus fails, the system can still operate at reduced capacity on the 
remaining bus. Synchronization of bus control channel messages between 
either processor 40 or 41 and any circuit pack is performed by the 
associated network control interface 46 or 41, respectively. The messages 
transmitted over a control channel may comprise the first five time slots 
of either TDM bus "A" or "B". Only one bus can carry control information 
at any one time, and in the event of failure, control information is 
carried on the other bus. The control channel operates in a master/slave 
configuration with the network control interface 46 or 51 as master and 
the circuits 54 through 58 as slaves. Each such circuit must have a unique 
address and can only communicate with the network control interface when 
granted permission. This protocol prevents collisions on the TDM bus 53, 
where two circuits might otherwise try to transmit simultaneously. 
In accordance with a preferred embodiment, the radio channel unit 54 shown 
in FIG. 3 is preferably a plug-in module containing all RF, baseband and 
control circuitry required to perform setup, locate or voice channel 
functions. The radio channel unit function as well as its operating 
channel, transmit power level, and other specific parameters are 
downloaded to each radio at initialization via the time division 
multiplexed bus 53 under control of the active processor 40 or 41. In 
addition, radio channel unit call processing algorithms are contained in 
nonvolatile memory circuits within each unit and may be updated via the 
time division multiplexed bus 53, if necessary. The down loadable 
parameter and nonvolatile memory update features advantageously allow 
remote reconfiguration of the radio channel unit and eliminate the need 
for many on-site visits. Also, the radio channel unit 54 contains built-in 
self test capabilities which are automatically executed at initialization 
and test results are reported to the radio control complex 31. 
The radio test unit 58 is used, primarily, to check the performance of the 
total RF path to and from receive and transmit antennas 23 and 22 (shown 
in FIG. 1). The basic circuit of the radio test unit 58 is similar to that 
of a radio channel unit 54, with a few differences. The radio channel 
units 54 have two inputs, one for each diversity; the radio test unit 58 
has only one. Another difference is in the RF switch control interfaces. 
On each radio channel unit shelf (32 in FIG. 2), the RF antenna selector 
switches associated with a channel unit are controlled via six parallel 
bit lines. Three bits are for the switches in the two receiver input 
diversity paths to each channel unit. The other three bits are for the 
switch in the transmit path. The radio test unit 58 controls RF switches 
located in the antenna interface frame 13. The radio test unit 58 contains 
a test receiver and test generator which serve to simulate a 
cellular/mobile subscriber unit. The test receiver can be tuned to any 
receive channel, and the test generator can be tuned to any transmit 
channel. Tuning is accomplished by commands sent by the time division 
multiplexed bus 53 to a transmit/receive frequency synthesizer (not shown) 
within the radio test unit 58. During receive testing on a cell site radio 
channel unit 54, the test generator within the radio test unit 58 is tuned 
to the channel under test, and the output of the test generator is applied 
to the appropriate cell site receiving antenna 23. Control is applied to 
the antenna interface frame 13 to select omni receive or one face of the 
directional antenna. 
In accordance with a preferred embodiment, all the data and voice 
communications between the MTSO 17 and the cell site 10 are based on a 
digital signaling format DS1 which is a bipolar return-to-zero signal at a 
1.544 Mb/s rate for T1-carrier. Alternatively, other digital signal 
formats may be used. The cell site data communication links 18 are 
selected, under the control of the communication processor interface 45 or 
50, to operate at 9.6 kb/s, 56 kb/s or 64 kb/s rates. A DS1 carrier link 
can accommodate 24 digital voice communication channels or a combination 
of digital voice and data channels. For each DS1 carrier, the radio 
channel frames 14, 15 and 16 must each have at least one DS1 interface 
circuit 57. Two data links are required between the primary radio channel 
frame 14 and the MTSO 17 for reliability. This is best accommodated via 
two DS1 carriers, with one data channel in each link. All cell site 
interfaces are digital, using DS1 boards with DS1 interface circuits. When 
the facility is a T1-carrier, the DS1 interface allows connection directly 
to the radio control units without the need for D4 channel banks. If 
analog facilities are used, D4 channel banks would, however, be required. 
The DS1 interface also allows connection directly to microwave systems or 
to fiber optic systems such as, for example, AT&T's fiber optics 
multiplexer DDM-1000. 
Although the present invention has been described in connection with 
particular embodiments thereof, additional embodiments, modifications and 
applications which will be apparent to those skilled in the art are 
included within the spirit and scope of the invention.