Spectrally efficient and high capacity acknowledgement radio paging system

An improved radio paging system providing automatic acknowledgment of message delivery, including a base station with spatially directive reception means and a pager capable of transmitting acknowledgment signals. The spatially directive reception means at the base station enhances the reception quality of the acknowledgment signals transmitted by the pager over that obtainable with conventional omnidirectional reception means, thereby compensating for the disparity in the base station and pager transmission powers.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to radio paging systems, and more particularly the 
invention relates to systems that implement an automatic mechanism for the 
confirmation of receipt of a paging message. 
2. Discussion of Prior Art 
The term "radio paging" refers to services in which messages, or "pages", 
are transmitted via radio, throughout a particular geographic area, to 
"pagers" in the possession of subscribers to this service. In the current 
art, these messages are broadcast digitally and contain short numeric 
(e.g. a phone number) or alphanumeric messages with length limitations on 
the order of tens of characters. 
A representative architecture for a paging system is depicted in FIG. 1. A 
page is initiated by a telephone or computer modem call through a wide 
area network interface 1, typically provided by the local telephone 
company, to the paging service provider's offices. This initial call 
specifies the message content and the address of the pager for which the 
message is intended. A paging controller 2 transmits the information 
associated with each page, via paging control links 3 (a,b,c), to base 
stations 5 (a,b,c) serving the target pager's geographic area. Each base 
station is responsible for providing radio paging coverage throughout a 
particular paging cell. Cell boundaries 4 (a,b,c) are determined by 
regulatory limits on emitted radio frequency energy and by local 
propagation effects. Information on pager locations is not maintained by 
the system. Each page is therefore broadcast omnidirectionally by all base 
stations in the target pager's geographic area in an attempt to assure 
successful delivery of the page. Users equipped with pagers are identified 
by a boxed "U" in the figure. Pagers continually monitor the base 
stations' transmission frequencies, and, when a pager detects a message 
incorporating its own address, that pager receives the message and 
displays it, most usually on an integral liquid crystal display or similar 
device. FIG. 2 depicts a pager 7 with integral display 8 and control keys 
9 (a, . . . ,d). 
Radio paging, as described above, has the following three key deficiencies: 
a) It is impossible for the paging system to determine whether or not a 
page has been received. A target pager might be outside the coverage area 
of the paging system, for example, or it might not be operating at the 
time that the page is transmitted. 
b) Existing paging systems provide no mechanism for direct subscriber 
response to a page. Most pages require some sort of response, but, in the 
current art, the subscriber must employ an alternative means of 
communication (e.g. a telephone call) to supply a response. 
c) Page message lengths are constrained to tens of bytes, limiting the 
utility of the paging system for detailed or lengthy messages. 
Deficiencies (a) and (b), above, stem from the unidirectional nature of the 
message flow in the system. Deficiency (c) stems from the paging 
provider's business need to serve a large number of customers in 
combination with limited spectrum availability and an omnidirectional 
radio transmission strategy. 
SUMMARY OF THE INVENTION 
Accordingly, several of the objects and advantages of the present invention 
are: 
a) to provide a paging system in which message receipt is automatically 
confirmed; 
b) to provide a paging system in which a subscriber can directly respond to 
paging messages by means of their pager; 
c) to provide a paging system in which message lengths are constrained to 
thousands, rather than tens, of bytes; 
d) to provide a paging system in which directive reception and directive 
transmission are employed at the base station to increase both the system 
capacity and achievable transmission rates beyond what is achievable with 
omnidirectional transmission and reception strategies; 
e) to provide a paging system in which automatic confirmation of message 
receipt is implemented with inexpensive, lightweight, compact pagers; 
f) to provide a paging system in which automatic confirmation of message 
receipt is implemented without auxiliary reception sites for data 
transmitted by the pager; and 
g) to provide a paging system with the preceding objects and advantages 
which is compatible with pagers that have no means for generating an 
acknowledgment, in particular pagers such as are employed in conventional 
paging systems in which automatic confirmation of message receipt does not 
occur. 
Still further objects and advantages will become apparent from a 
consideration of the ensuing description and drawings.

LIST OF REFERENCE NUMERALS 
1. Wide area network interface 
2. Paging controller 
3a. Paging control link 
3b. Paging control link 
3c. Paging control link 
4a. Paging cell boundary 
4b. Paging cell boundary 
4c. Paging cell boundary 
5a. Paging base station 
5b. Paging base station 
5c. Paging base station 
6. High speed message link 
7. Pager 
8. Pager liquid crystal display 
9a. Pager control button 
9d. Pager control button 
10. Base station controller 
11. Demodulated received signal 
12. Spatially demultiplexed received signal 
13. Received signals 
14. Demultiplexing weights 
15. Data to be transmitted directionally 
16. Modulated signal to be multiplexed for transmission 
17. Modulated, spatially multiplexed signals to be transmitted 
18. Multiplexing weights 
19. Spatial processor 
20. Spatial controller 
21. Messages to be omnidirectionally transmitted 
22. Broadcast modulator/transmitter 
23. Multichannel transmitters 
24. Multichannel receiver 
25a. Multichannel receiver 
25m. Multichannel receiver 
26a. Multichannel transmitter 
26m. Multichannel transmitter 
27. Omnidirectional transmission antenna 
28a. Transmission antenna 
28m. Transmission antenna 
29a. Reception antenna 
29m. Reception antenna 
30. Spatial demultiplexer 
31. Spatial multiplexer 
32. Signal modulator 
33. Signal demodulator 
34. Spatial control data 
35. Spatial parameter data 
36. Common receiver oscillator 
37. Received data buffer 
38. Delayed received signals 
39. Receiver control data 
40. Transmitter control data 
41. Common transmitter oscillator 
42. Pager antenna 
43. Pager duplexer 
44. Pager duplexer output 
45. Pager receiver 
46. Pager received signal 
47. Pager demodulator 
48. Pager demodulated received signal 
49. Pager keyboard and keyboard controller 
50. Pager keyboard data 
51. Pager display data 
52. Pager display and display controller 
53. Pager modulator 
54. Pager data to be transmitted 
55. Pager modulated data to be transmitted 
56. Pager transmitter 
57. Pager transmitter output 
58. Pager transmitter control data 
59. Pager receiver control data 
60. Pager central processing unit 
DESCRIPTION OF THE SPECIFIC EMBODIMENT 
FIG. 3 depicts a preferred embodiment of base station apparatus in 
accordance with the invention. A paging control link 3a carries messages 
between the base station equipment and the paging controller. These 
messages consist of instructions for the base station to issue a page, and 
indications to a paging controller 2 that the base station has 
successfully delivered a page or that the base station was unable to 
deliver a particular page. A base station controller 10 acts as the 
interface between the base station and paging control link 3a, and serves 
to coordinate the overall operation of the base station. Base station 
controller 10 is implemented with a conventional central processing unit 
along with memory and interfaces to paging control link 3a. 
Three classes of radio messages are distinguished in the system, and base 
station controller 10 serves as a nexus for all radio messages. The first 
class consists of messages that are broadcast omnidirectionally from the 
base station. There are two messages in this class: pages intended for 
conventional pagers that are unable to provide acknowledgment, and message 
channel assignment messages for pagers capable of providing message 
acknowledgment. Baseband messages in this class 21 are communicated to an 
omnidirectional broadcast modulator/transmitter 22 which, in turn, drives 
an omnidirectional transmission antenna 27. 
The second class of radio messages consists of acknowledgments transmitted 
by pagers and directionally received at the base station. These messages 
consist of data identifying the originating pager and either an 
acknowledgment or data specified by the operator of the pager in response 
to a page. These radio transmissions impinge on a number, m, of reception 
antennas 29(a, . . . ,m) each of whose output is connected to one of m 
multichannel receivers in a bank of phase-coherent multichannel receivers 
24. FIG. 4 depicts individual multichannel receivers 25(a, . . . ,m) with 
antenna connections, a common local receiver oscillator 36, and digital 
outputs. In the present embodiment, multichannel receivers 25(a, . . . ,m) 
all operate on a single common frequency band. In an alternate embodiment, 
multichannel receivers 25(a, . . . ,m) operate on a common multiplicity of 
frequency bands. Common local receiver oscillator 36 ensures that the 
signals from reception antennas 29(a, . . . ,m) are coherently 
down-converted to baseband; its frequency is controlled by a spatial 
processor 19 (FIG. 3) via receiver control data 39. Referring again to 
FIG. 3, received signals 13 from each multichannel receiver 25(a, . . . 
,m) are available to spatial processor 19 and to a received data buffer 
37. Received data buffer 37 consists of m parallel "first-in first-out" 
arrangements of digital memory producing delayed received signals 38 which 
are delayed, but otherwise identical, copies of received signals 13. 
Spatial processor 19 consists of a central processing unit and receives 
received signals 13 and certain spatial parameter data 35 from a spatial 
controller 20. Spatial processor 19 produces certain spatial parameter 
data 35, spatial demultiplexing weights 14, spatial multiplexing weights 
18, receiver control data 39 and transmitter control data 40. 
A spatial demultiplexer 30 linearly combines delayed received signals 38, 
according to spatial demultiplexing weights 14 as depicted in FIG. 5. 
Arithmetic operations in spatial demultiplexer 30 are carried out using 
general purpose arithmetic chips. The notations "s.sub.1 " and "s.sub.m " 
in the figure denote the first and m.sup.th signal components of delayed 
received signals 38, respectively. The notations "w.sub.l " and "w.sub.m " 
in the figure denote the first and m.sup.th weight components of spatial 
demultiplexing weights 14, respectively. Referring again to FIG. 3, the 
output of spatial demultiplexer 30 is a spatially demultiplexed received 
signal 12 which is demodulated by a signal demodulator 33 producing a 
demodulated received signal 11. Demodulated received signal 11 and 
corresponding spatial control data 34 are available to base station 
controller 10. 
The third class of radio messages consists of paging data (i.e. the page, 
itself) which are directionally transmitted from the base station to the 
pager. Base station controller 10 in FIG. 3 provides data to be 
transmitted 15 to a signal modulator 32, and associated spatial control 
data 34 to spatial controller 20. The output of signal modulator 32 is a 
modulated signal to be multiplexed for transmission 16. 
Modulated signal 16 and a set of spatial multiplexing weights 18 are 
combined in a spatial multiplexer 31 to produce m weighted versions of 
modulated signal 16 as depicted in FIG. 6. The notations "w.sub.l " and 
"w.sub.m " in the figure denote the first and m.sup.th weight components 
of spatial multiplexing weights 18, respectively. These weighted signals 
constitute a collection of modulated and spatially multiplexed signals to 
be transmitted 17. Arithmetic operations in spatial multiplexer 31 are 
carried out using general purpose arithmetic chips. Modulated and 
spatially multiplexed signals 17 are inputs to a bank of m phase coherent 
multichannel transmitters 23. FIG. 7 depicts individual multichannel 
transmitters 26(a, . . . ,m) with antenna connections, a common local 
transmitter oscillator 41, and digital inputs. In the present embodiment, 
multichannel transmitters 26(a, . . . ,m) all operate on a single common 
frequency band. In an alternate embodiment, multichannel transmitters 
26(a, . . . ,m) operate on a common multiplicity of frequency bands. 
Common local transmitter oscillator 41 ensures that the relative phases of 
spatially multiplexed signals 17 are preserved during transmission by 
transmission antennas 28(a, . . . ,m). The frequency of common local 
transmitter oscillator 41 is controlled by spatial processor 19 (FIG. 3) 
via transmitter control data 40. 
FIG. 8 depicts the component arrangement in pager 7. A pager antenna 42 is 
connected to a pager duplexer 43 to permit pager antenna 42 to be used for 
both pager transmission and reception. In one alternate embodiment, pager 
duplexer 43 would be replaced by a transmit-receive switch. A pager 
duplexer output 44 serves as input to a pager receiver 45. Pager receiver 
45 produces a down-converted signal 46 which is the input to a pager 
demodulator 47. A pager demodulated received signal 48, estimated message 
bits, serves as one input to a pager central processing unit 60. Pager 
central processing unit 60 is implemented with a standard microprocessor. 
Pager central processing unit 60 also produces pager receiver control data 
59 for selecting the pager's reception channel, pager transmitter control 
data 58 for selecting the pager's transmission channel, pager data to be 
transmitted 54, and pager display data 51 for a pager display and display 
controller 52. Pager central processing unit 60 also receives pager 
keyboard data 50 from a pager keyboard and keyboard controller 49. Pager 
data to be transmitted 54 is input to a pager modulator 53 producing a 
pager modulated signal to be transmitted 55. Pager modulated signal to be 
transmitted 55 is up-converted and amplified in a pager transmitter 56, 
producing a pager transmitter output 57. Pager transmitter output 57 is 
then input to pager duplexer 43. 
Operation of Invention: 
General Principles--Base Station: 
Paging base station 5a (FIG. 3), along with other paging base stations in 
the system, processes many pages simultaneously. FIGS. 9A and 9B provide a 
flow chart for the processing of a page at base station 5a, thereby 
illustrating the general operating principles of the invention. 
Instructions to issue a page are delivered to base station 5a over paging 
control link 3a. Each such instruction includes a numeric identifier that 
uniquely specifies the pager that is to be the recipient of the message, 
an indication as to whether the targeted pager is capable of generating an 
acknowledgment, and the data to be transmitted to the targeted pager. 
Processing then proceeds from the block labeled "Begin" in FIG. 9A. 
If the instructions for this page indicate that the targeted pager is 
incapable of generating an acknowledgment (i.e., it is a conventional 
pager), base station controller 10 passes the pager identifier and the 
data to be broadcast to broadcast modulator/transmitter 22 for 
omnidirectional broadcast, ending the paging cycle for this type of page. 
The radio channel employed by broadcast modulator/transmitter 22 will be 
referred to as the "broadcast channel" in the sequel. Similarly, the radio 
channels employed by multichannel transmitters 23 will be referred to as 
"message channels", and those employed by multichannel receivers 24 will 
be referred to as "acknowledgment channels". 
If, on the other hand, the instructions for the page indicate that the 
targeted pager is capable of generating an acknowledgment, a different 
paging cycle ensues, as depicted in the flow chart. In this case, base 
station controller 10 prepares a message channel assignment message and 
passes the data for this message, which includes the targeted pager's 
identifier, to broadcast modulator/transmitter 22 for omnidirectional 
broadcast on the broadcast channel. The purpose of the message channel 
assignment message is to command the target pager to tune to the specified 
message channel for the remainder of the paging cycle. Each message 
channel has an associated acknowledgment channel. 
Immediately following the issuance of this message channel assignment 
message, base station controller 10 initializes a retry counter, the value 
of which is denoted by n.sub.r, to zero, and a timer which generates an 
alarm after the passage of w.sub.a seconds. If that alarm occurs prior to 
the receipt of a corresponding acknowledgment (abbreviated to "ACK" in the 
flow chart), n.sub.r is incremented by one; and, if a pre-specified limit 
on the number of retry attempts for a message channel assignment has not 
been exceeded, the message channel assignment message is resent. If the 
retry attempt limit has been exceeded, the page is considered unsuccessful 
and the paging cycle terminates as indicated in the flow chart. 
Simultaneously with the issuance of the message channel assignment message, 
base station controller 10 alerts spatial controller 20 that an 
acknowledgment is expected on the selected acknowledgment channel. Spatial 
controller 20 provides this information to spatial processor 19 which then 
selects the current acknowledgment channel by providing appropriate 
receiver control data 39 to multichannel receivers 24. Spatial processor 
19 then monitors received signals 13 to detect the presence of the pager's 
acknowledgment and to estimate the pager's direction with regard to base 
station 5a. When an incoming acknowledgment is detected, spatial processor 
19 calculates and provides appropriate demultiplexing weights 14 to 
spatial demultiplexer 30 and, simultaneously, provides the pager's 
direction to base station controller 10, via spatial controller 20, for 
association at base station controller 10 with demodulated pager 
acknowledgment 11 generated by signal demodulator 33. Descriptions of the 
operations performed internally by spatial processor 19, spatial 
demultiplexer 30, and spatial multiplexer 31 are provided later in this 
section. 
Having received the pager's acknowledgment and direction relative to base 
station 5a, as shown in FIG. 3 base station controller 10 supplies message 
data 15 for the page to signal modulator 32 and, simultaneously, supplies 
the associated pager's direction and message channel to spatial controller 
20. The pager's direction and message channel are then supplied to spatial 
processor 19. Spatial processor 19 provides transmitter control data 40 to 
multichannel transmitters 23 to set the message channel. Spatial processor 
19 also generates spatial multiplexing weights 18 for spatial multiplexer 
31 corresponding to the pager's direction. Modulated, spatially 
multiplexed signals 17 are thereby provided to multichannel transmitters 
23 for transmission from transmission antennas 28(a, . . . ,m). 
Immediately following transmission of the message portion of the page, 
spatial processor 19 issues receiver control data 39 to multichannel 
receivers 24 causing multichannel receivers 24 to tune to the 
corresponding acknowledgment channel. Simultaneously, spatial processor 19 
provides appropriate demultiplexing weights 14 to spatial demultiplexer 30 
for directional reception of a pager-generated acknowledgment of the 
message portion of the page. Base station controller 10 monitors 
demodulated received signal 11 for the pager acknowledgment. 
Base station controller 10, immediately following issuance of the message 
data transmission for a particular page, initializes a retry counter as 
shown in FIG. 9B, the value of which is denoted by n.sub.r, to zero, and a 
timer which generates an alarm after the passage of w.sub.r seconds. If 
that alarm occurs prior to the receipt of an acknowledgment (abbreviated 
to "ACK" in the flow chart) from the target pager, as determined by 
monitoring of demodulated received signal 11, n.sub.r is incremented by 
one. If a pre-specified limit on the number of retry attempts for a 
message data transmission has not been exceeded, the message data 
transmission and acknowledgment cycle, as described in the preceding two 
paragraphs, is repeated. If the retry attempt limit has been exceeded, the 
page is considered unsuccessful and the paging cycle terminates as 
indicated in the flow chart. If an acknowledgment from the targeted pager 
is received before the number of retry attempts has been exceeded, 
however, the page is considered successful and the paging cycle 
terminates. In all instances when the target pager is capable of 
generating acknowledgments, base station controller 10 apprises paging 
controller 2 of the success of the page via paging control link 3a. If 
base station controller 10 considers the page to have been a success, it 
also apprises paging controller 2 of the target pager's estimated 
location. 
General Principles--Pager: 
The preceding paragraphs describe the paging cycle as executed at base 
station 5a. The complementary operations performed by pager 7 are now 
described with reference to FIG. 8. Pager 7 operates in a standby mode 
whenever it is not actively processing a page. In this standby mode, pager 
receiver 45 is tuned to one or more well-known paging frequencies by pager 
central processing unit 60 enabling pager demodulator 47 to demodulate all 
message channel assignment messages. Pager central processing unit 60 
parses these demodulated messages, remaining in this standby mode unless 
it detects its own unique numeric identifier in one of the messages. 
Upon detection of its own unique numeric identifier in a message channel 
assignment message, pager central processing unit 60 tunes pager 
transmitter 56 to the corresponding acknowledgment radio channel, and 
passes an acknowledgment message containing its own unique numeric 
identifier to pager modulator 53 for transmission via pager antenna 42. 
Pager central processing unit 60 then tunes pager receiver 45 to the 
assigned message channel by producing appropriate pager receiver control 
data 59. Pager central processing unit 60 simultaneously initializes a 
timer which generates an alarm at the end of an interval commensurate with 
the values of w.sub.r and the message transmission retry attempt limit 
employed by base station controller 10 as described above. If the alarm 
occurs before pager central processing unit 60 detects a complete message 
transmission in pager demodulated received signal 48, pager 7 returns to 
standby mode. If, on the other hand, pager central processing unit 60 
detects a complete message transmission in pager demodulated received 
signal 48, pager central processing unit 60 transmits a second 
acknowledgment in the manner described above. Once this acknowledgment has 
been transmitted, pager central processing unit 60 downloads the 
demodulated message data to pager display and display controller 52 for 
display, and returns to standby mode. 
While in standby mode, pager keyboard and keyboard controller 49 may be 
used to cause pager central processing unit 60 to issue commands to pager 
display and display controller 52 causing the display to "scroll" through 
any messages stored at pager 7. 
Spatial Processing--Base Station: 
Spatial processing at base station 5a (FIG. 3) is conducted using the 
methods described in co-pending application Ser. No. 07/806,695, supra 2. 
The operations performed by spatial processor 19 are described therein, as 
is the operation of spatial multiplexer 31 and the operation of spatial 
demultiplexer 30. Also described therein, are methods for effecting 
simultaneous paging cycles for multiple target pagers with a single 
acknowledgment and message channel pair, and for effecting simultaneous 
paging cycles for multiple target pagers on multiple acknowledgment and 
message channel pairs. 
In contrast to the invention described in the co-pending application, 
received data buffer 37 effects a digital delay line for received signals 
13 of duration equal to the time period for spatial updates in spatial 
processor 19. Demultiplexing weights 14 are thereby applied to the 
identical time period of received signals 13 employed for spatial 
environment estimation. This signal processing strategy is necessitated by 
the short time duration of acknowledgment messages generated by pager 7. 
Alternate Embodiments 
Shared Transmit and Receive Arrays: 
In one alternate embodiment, transmission antennas 28(a, . . . ,m) and 
reception antennas 29(a, . . . ,m) at base station 5a are replaced by a 
single array of m antennas. Each element in this array is attached to both 
its respective component of multichannel transmitters 23 and its 
respective component of multichannel receivers 24 by means of a duplexer. 
Omnidirectional Message Channel: 
In one alternate embodiment, message channel transmissions are performed in 
an omnidirectional fashion rather than in the directional fashion 
described above. In this embodiment, spatial multiplexer 31, multichannel 
transmitters 23 and transmission antennas 28(a, . . . ,m) are replaced by 
a single transmitter and antenna. Base station controller 10 issues 
appropriate transmitter control information 40 in this embodiment. 
Broadcast Channel Transmitted from an Array Element: 
In one alternate embodiment, broadcast channel transmissions are performed 
using one of transmission antennas 28(a, . . . ,m). In this embodiment, 
the respective multichannel transmitter 26a, for example, has an output 
power rating comparable to that of broadcast modulator/transmitter 22 
which is typically m.sup.2 greater than that of the other m-1 multichannel 
transmitters in the array. In one such embodiment, broadcast channel 
transmissions and message channel transmissions are interleaved. In 
another such embodiment, broadcast channel transmissions and message 
channel transmissions are performed simultaneously. 
In this embodiment, broadcast modulator/transmitter 22 and omnidirectional 
transmission antenna 27 are eliminated from base station 5a. 
Swept Page: 
In one alternate embodiment, broadcast channel messages are transmitted 
using all of transmission antennas 28(a, . . . ,m). Broadcast channel 
messages to be transmitted are placed in a "first-in, first-out" queue. 
Spatial processor 19 transmits these broadcast channel messages by 
creating a directional beam (an array transmission pattern which is 
designed to concentrate transmitted radio frequency energy in a narrow 
angular sector and to minimize transmitted energy outside of that sector, 
as is well known in the art of phased antenna arrays) and transmitting the 
first paging message in the queue by means of the beam. Following that 
transmission a new directional beam, covering the next angular sector of 
approximately the same angular width in a clockwise direction, is created 
and the paging message is transmitted again. This process is repeated 
until the earlier of the page's transmission throughout the base station's 
coverage region or the receipt of an acknowledgment from the target pager. 
If additional broadcast channel messages are in the queue, the next 
message is then extracted from the queue and transmitted using the same 
strategy. This "swept page" strategy can occur simultaneously with the 
delivery of message channel messages described in the primary embodiment. 
In addition, if multiple broadcast channels are employed, swept pages can 
be performed simultaneously, on all broadcast channels. 
In this embodiment, broadcast modulator/transmitter 22 and omnidirectional 
transmission antenna 27 are eliminated from base station 5a. 
User Equipment: 
In one alternate embodiment, the user equipment is more general than pager 
7. The user equipment in this case is a "personal organizer", "personal 
digital assistant", or laptop computer incorporating, through a 
combination of software and hardware, equivalent functionality to pager 7. 
This user equipment could additionally support the transmission and 
reception of message data other than alphanumeric messages, as is well 
known in the art. These other types of data might include digitized voice 
and facsimile data. PCMCIA cards and associated software serving this 
purpose are currently available for existing paging systems. 
Message Acknowledgments Incorporating User Responses: 
In one alternate embodiment, users can cause one of several predetermined 
responses to be incorporated in the message acknowledgment generated by 
pager 7. In this embodiment, each message transmitted to the pager 
includes a list of possible responses selected by the originator of the 
message. Pager 7, detecting the presence of this list in the data 
transmitted to it, presents the list to the user via pager display and 
display controller 51. Using pager keypad and keypad controller 49, the 
user indicates which item from the fixed list of responses is to be 
returned with the acknowledgment. The index of this item is encoded in the 
acknowledgment and, at base station 5a, this index is provided to paging 
controller 2 via paging control link 3a, along with a unique identifier 
for the target pager. 
Pager Message Initiation: 
In one alternate embodiment, pager 7 can initiate a page. Using pager 
keypad and keypad controller 49, the user enters the unique identifier of 
the recipient's communications equipment and the message data. Pager 7 
then transmits a message on the acknowledgment channel indicating that it 
wishes to send a page, this message is received directionally by base 
station 5a. Upon receipt of this request, base station 5a directionally 
transmits an acknowledgement to the originating pager on the message 
channel. Upon receipt of this acknowledgment, pager 7 transmits the 
message data and unique identifier of the recipient's pager on the 
acknowledgment channel. Upon receipt of this data, base station controller 
10 forwards the message data and unique identifier of the recipient's 
communications equipment to paging controller 2 via paging control link 
3a. The processing of this request for a page at paging controller 2 then 
proceeds in the usual fashion for a page request. 
Pager Location Registration: 
In one alternate embodiment, pager 7 associates itself with one of base 
stations 5(a,b,c). In this embodiment, each of base stations 5(a,b,c) 
periodically transmits a unique base station identifier on its respective 
broadcast channel. Pager 7 incorporates a general memory register for 
storing a base station identifier. Pager 7, upon being turned on, 
initializes this register to a reserved value used by no base station as 
its unique identifier. Following this initialization, whenever pager 7 is 
in the standby mode described above it decodes all base station 
identifiers that it detects in the broadcast channels which it is 
monitoring. In the event that pager 7 detects several identical and 
consecutive base station identifiers that differ from its internally 
stored base station identifier, pager 7 updates its internally stored base 
station identifier to this new detected value and transmits a message on 
the acknowledgment channel including its own unique identifier and the new 
base station identifier. Each of base stations 5(a,b,c) which 
directionally receives this message, forwards the pager identifier and 
base station identifier contained in the message to paging controller 2 
via its respective base station controller 10. 
Use of Transaction Identifiers: 
In one alternate embodiment, a short numeric transaction identifier is 
generated by base station controller 10 for each of the paging cycles 
depicted by the flowchart of FIGS. 9A and 9B. The only requirement on the 
values of the set of current transaction identifiers employed by base 
station controller 10 is that each active transaction identifier uniquely 
correspond to an active paging cycle. The transaction identifier is used 
in the following manner with pagers capable of generating an 
acknowledgment. The initial message channel assignment message depicted in 
FIG. 9A includes the transaction identifier along with the target pager's 
numeric identifier and message channel assignment. All subsequent 
transmissions for that particular paging cycle, emanating from either base 
station 5a or the pager 7, are tagged with the assigned transaction 
identifier rather than the numeric identifier of pager 7 as described in 
the principal embodiment. 
Thus, while the invention has been described in detail with reference to 
one embodiment, the description is illustrative of the invention and is 
not to be construed as limiting the invention. Various modifications and 
applications may occur to those skilled in the art without departing from 
the true spirit and scope of the invention as defined by the appended 
claims.