Radio conference system and terminal unit therefor

In a radio conference system of the present invention, a hub station 1 sends information to a plurality of terminal stations 2 while adding an error checking code thereto. The terminal stations 2 each sends, on detecting an error out of the information received from the hub station 1, a resend request signal including an ID (Identification) code assigned to the terminal station. The hub station 1 counts the number of times of receipt of the resend request signal on a terminal station basis. When the number of the resend request signals received from any one of the terminal stations 2 exceeds a preselected value, the hub station 1 displays alarm information indicative of the above terminal station.

BACKGROUND OF THE INVENTION 
The present invention relates to a radio conference system in which a hub 
station and a plurality of terminal stations interchange data with each 
other and, more particularly, to a terminal unit guiding technology for 
insuring a high transmission efficiency between the terminal stations and 
the hub station. 
Some different transmission protocols have been proposed for a radio 
conference system in order to implement sure communication and high 
transmission efficiency between a single hub station and a plurality of 
terminal stations. For example, a polling system allows a hub station to 
send data to terminal stations and then confirm receipt terminal station 
by terminal station. Another system allows the individual terminal station 
to detect an error out of data received from a hub station and return a 
resend request signal (NAK) to the hub station. Further, a receipt 
terminal may include a display for displaying communication quality 
between it and a hub station in terms of a receipt electric field 
strength. 
However, the conventional schemes described above each has some problems 
left unsolved, as follows. Although sure transmission is expected with the 
polling system, polling wastes time when it comes to a conference system 
in which radio communication is used at a visible distance. Specifically, 
this kind of conference system does not need strict confirmation of 
transmission and receipt because most terminal stations are given 
acceptable communication quality. Therefore, causing all the terminal 
stations to acknowledge receipt by polling needs an extra period of time 
and lowers the data transfer efficiency. 
The NAK scheme saves the above station-by-station polling time by 
determining that a terminal station having returned no NAK signals within 
a preselected period of time has received data correctly. However, the 
problem with the NAK scheme is that when any one of many terminal stations 
is put in a low wave propagation condition, the hub station repeats 
resending exclusively for such a terminal station. Therefore, the hub 
station cannot send the next data to the terminal stations until it ends 
the resending operation meant for the terminal station in question, i.e., 
until it sends the data to all the terminal stations. As a result, if at 
least one of the terminal stations is of low propagation quality, the 
overall transmission efficiency of the system falls. 
The display scheme capable of displaying the receipt electric field allows 
each terminal unit to be moved to a location where the wave propagation 
quality is relatively high in accordance with the display. Such mobility 
of the terminal unit increases the overall data transfer efficiency of the 
entire system. However, it is not easy even for an expert in the radio 
communications art to determine the degree of the receipt electric field 
strength which insures error-free data transmission. Moreover, in the case 
of packet transmission, the measurement of the electric field strength 
itself is sometimes difficult because the hub station does not always send 
an electromagnetic wave continuously. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a radio 
conference system capable of guiding the participants of a radio 
conference and carrying terminal stations to adequate locations in 
relation to a hub station, and thereby enhancing the efficient data 
distribution from the hub station to the terminal stations. 
In accordance with the present invention, a radio conference system has a 
hub station and a plurality of terminal stations each being capable of 
receiving data from the hub station. The hub station includes a 
distributing section for distributing information consisting of data and 
an error checking code to the terminal stations, a resending section for 
identifying, on receiving a resend request signal from any one of the 
terminal stations, the terminal station sent the resend request signal, 
and then resending the information, a plurality of counters respectively 
assigned to the terminal stations each for counting the resend request 
signals received from the terminal station associated therewith, and an 
alarming section for displaying alarm information indicative of the 
terminal station associated with the counter whose count has exceeded a 
preselected count. The terminal units each includes a detecting section 
for detecting an error out of the information sent from the hub station, 
and a resend request sending section for sending, when the detecting 
section detects an error, the resend request signal including 
identification information identifying the terminal station. 
In the above system, a chairman operating the hub station can urge a 
participant carrying the displayed terminal station to move to a location 
where the wave receipt condition is better. As a result, the frequency of 
generation of the resend request signal is successfully reduced, and the 
overall transmission efficiency of the system is enhanced. 
Further, in accordance with the present invention, a radio conference 
system also has a hub station, and a plurality of terminal stations each 
being capable of receiving information from the hub station. The hub 
station includes a distributing section for distributing information 
consisting of data and an error checking code to the terminal stations, 
and a resending section for resending the information on receiving a 
resend request signal from any one of the terminal stations. The terminal 
stations each includes a detecting section for detecting an error out of 
the information received from the hub station, a resend request sending 
section for sending, when the detecting section detects an error, the 
resend request signal including identification information identifying the 
terminal station, a counter for counting the resent request signals sent, 
and an alarming section for displaying alarm information showing that a 
count of the counter has exceeded a preselected count. 
In the above system, a participant holding the terminal station with the 
alarm information can move to a location of better wave receipt condition 
spontaneously. This also lowers the frequency of generation of the resend 
request signal and thereby enhances the overall transmission efficiency of 
the system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1 of the drawings, a radio conference system embodying 
the present invention is shown and includes a hub station 1 and a terminal 
station 2. As shown, the hub station 1 and terminal station 2 are 
identical in configuration, i.e., they are identical terminal units. One 
of the two terminal units 1 and 2 held by the chairman of a conference 
plays the role of a hub station while the other terminal unit held by a 
participant plays the role of the terminal station. In this sense, the 
distinction between the hub station and the terminal station is only a 
matter of convenience. 
The hub station 1 includes an operation/display section 11 for allowing 
data necessary for the terminal itself to be input thereon, while 
displaying received data. A radio section 13 sends data or receives data 
via an antenna 14. A first memory (MEM) 15 stores data to be sent or data 
received from another terminal unit for a moment. A second memory (MEM) 16 
stores data for estimating the receiving states of terminal stations. A 
control section 12 executes control which will be described. The terminal 
station 2 has the same construction as the hub station 1, as mentioned 
earlier. 
A single hub station 1 is selected by the chairman of a conference on the 
operation/display section 1. The control section 12 of the terminal unit 
to play the role of the hub station causes the terminal unit to operate in 
a hub station mode and causes each of the other terminal units to operate 
in a terminal station mode. 
The terminal station 2 is a portable unit carried by the participant of a 
conference; in practice, a plurality of terminal stations are each held by 
one of a plurality of participants. While the chairman and participants 
are generally positioned within earshot, the range of earshot may not 
coincide with the range of propagation of an electromagnetic wave, 
depending on the conditions of a conference room or the ability of a radio 
system used for a conference. 
FIG. 2 demonstrates resend control particular to radio transmission which 
allows identical information to be sent to a plurality of terminal 
stations at the same time. The control section 12 of the hub station 1 
divides information to be distributed and stored in the memory 15 
beforehand into a plurality of blocks, adds a CRC (Cyclic Redundancy 
Check) or similar error checking code to each block of information, and 
then broadcasts the information via the radio section 13 and antenna 14 
block by block. 
FIG. 2 shows the resend control beginning with the step of broadcasting 
information a as a single transmission block. As shown, terminal stations 
A and B (representative of a plurality of terminal stations) each receives 
one block of information from the hub station or terminal 1. In response, 
the terminal stations A and B each causes its control section 12 to 
determine whether or not a transmission error has occurred in the received 
information a on the basis of the CRC code. If the information a is free 
from errors, the terminal station A or B writes the information in the MEM 
15 and then waits for the next block of data from the hub station 1. At 
this instant, the terminal station A or B that received the error-free 
information does not inform the hub station 1 of the receipt of the 
correct information, as indicated by a dashed line (OK) in FIG. 2. This is 
because the probability of error-free transmission is high with a 
conference system in which a number of terminal stations gather in the 
same environment of relatively high wave propagation quality; returning an 
acknowledgement each time would simply waste time. However, when a control 
section 12 detect an error in the received information, the terminal 
station A or B including that control section 12 returns a NAK signal to 
the hub station 1 until it receives the information correctly. 
In FIG. 2, it is assumed that the terminal station A has detected an error 
in the received information a and returned the NAK signal while the 
terminal station B has received the information a correctly. On receiving 
the NAK signal within a preselected period of time t since the 
broadcasting of the information a, the hub station 1 again broadcasts the 
same information a (resending). FIG. 2 shows a condition wherein the 
terminal station A receives the resent information correctly and therefore 
does not return the NAK signal, and then the hub station 1 broadcasts the 
next block of information b on the elapse of the next period of time t. In 
FIG. 2, both the terminal stations A and B are assumed to receive the 
information b correctly. 
The resending system illustrated in FIG. 2 is a remedy against the 
temporary disturbance to the propagation of an electromagnetic wave. The 
problem is that any one of the terminal stations may continuously generate 
the NAK signal because it is located at a position where the receipt 
condition is poor; then, the hub station would repeat resending without 
broadcasting the next information. While this problem may be solved if the 
number of times of resending is limited, even such an implementation 
lowers the overall transmission efficiency of the system including many 
other terminal stations. 
The continuous generation of the NAK signal by a certain terminal station 
means that the wave propagation condition between the terminal station and 
the hub station is poor. The best solution to the above problem is to, if 
the terminal station is mobile, cause the terminal station to move to a 
position of good wave propagation condition. This can be done if the 
participant carrying the terminal station in question is informed of the 
continuous generation of the NAK signal and urged to move to an adequate 
position. Two different procedures for urging the above participant to 
move to the adequate position will be described hereinafter. 
A first procedure is executed by the hub station 1, FIG. 1, as follows. For 
this procedure, the hub station 1 includes counters each assigned to a 
particular terminal station. The counters each indicates the number of 
times of receipt of the NAK signal from the associated terminal station on 
the basis of a terminal ID code included in the NAK signal. Every time the 
hub station 1 receives the NAK signal from any one of the terminal 
stations, it increments the counter assigned to that terminal station by 1 
(one). When the counter reaches a preselected value, the hub station 1 
displays the ID code assigned to the above terminal unit together with an 
alarm on the operation/display section 11. At the same time, the hub 
station 1 may advantageously output an alert in the form of vibration or 
tone because the chairman may not be watching the display section 11 by 
accident. 
The chairman, watching the alarm appearing on the hub station 1, urges the 
participant carrying the terminal station in question to move to a 
position of good wave propagation condition. If desired, the ID codes and 
the names of the participants may be registered in the hub station 1 
beforehand in one-to-one correspondence, so the ID code for alarming can 
be replaced with the participant's name. After alarming the participant, 
the hub station 1 causes its control section 12 to reset the counter 
reached the preselected value. Alternatively, the chairman may reset the 
counter on the operation/display section 11. 
The above control is executed by the control section 12 implemented as, 
e.g., a microprocessor. A program for the microprocessor is stored in a 
ROM (Read Only Memory) or similar storage, not shown, beforehand. 
The operation of the control section 12 included in the hub station 1 and 
that of the control section 12 included in each terminal station in 
accordance with the first procedure will be described more specifically 
with reference to FIG. 3. The two stations 1 and 2 shown in FIG. 1 can 
each play the role of a hub station or a terminal station, depending on 
the operation mode set on the operation/display section 11, as stated 
earlier. As shown in FIG. 3, the control section 12 of each terminal 
station 1 or 2 determines whether or not a hub station mode command has 
been input on the operation/display section 11 (step S101). If the answer 
of the step S101 is positive (Y), the control section 12 executes a 
sequence of steps S102 through S109. If the answer of the step S101 is 
negative (N), meaning that the control section 12 should set up a terminal 
station mode, it executes a sequence of steps S110 through S112. 
Consequently, the control section 12 of the hub station 1 executes the 
steps S102 through S109 while the control section 12 of the terminal 
station 2 executes the steps S110 through S112. 
Specifically, the control section 12 of the hub station 1 resets all the 
counters C(i) (i=1, 2, . . . , I; I being the number of terminal stations) 
respectively assigned to the terminal stations (step S102). Then, the 
control section 12 reads one block of data to be distributed out of the 
MEM 15, adds a block number, error checking code and so forth to the 
block, and then delivers them to the radio section 13. The radio section 
13 broadcasts the input data to all the terminal stations via the antenna 
104 (step S103). Subsequently, the control section 12 determines whether 
or not the NAK signal has been received from any one of the terminal 
stations within the period of time t since the transmission of the data 
(step S104). If the answer of the step S104 is N, the control section 12 
returns to the step 103 so as to broadcast the next block of data. 
If the answer of the step S104 is Y, the control section 12 of the hub 
station 1 again causes the radio section 13 to broadcast the same data 
(step S105), and increments the counter C(j) assigned to the terminal 
station j sent the NAK signal by 1 (step S106). Then, the control section 
12 determines whether or not the count of the counter C(j) has exceeded a 
preselected threshold TH (step So). If the answer of the step So is 
negative, the program returns to the step S104 to see if the terminal 
station j has again sent the NAK signal in response to the resent data or 
not. When the counter C(j) exceeds the threshold TH (Y, step So), the 
control section 12 displays an alarm relating to the terminal station j on 
the operation/display section 11 (step 108). Thereafter, the control 
section 12 resets the counter C(j) (step 109), returns to the step S104, 
and then determines whether or not the terminal station has again sent the 
NAK signal in response to the data resent in the step S105. 
On the other hand, the control section 12 of the terminal station 2 
receives the data sent from the hub station 1 via the radio section 13 
(step S110). The control section 12 neglects the received data if the data 
is the resent data and if the terminal station 12 has already received the 
same data correctly. This decision can be done on the basis of the block 
number included in the receive data. Subsequently, the control section 12 
determines, based on the error checking code added to the data, whether or 
not the received data is correct (step S111). If the answer of the step 
S111 is Y, the control section 12 writes the received data in the MEM 15 
(step S112) and then returns to the step S110 for waiting for the next 
data. If the received data includes an error, as determined in the step 
S111, the control section 12 sends the NAK signal to the hub station 1 
(step S113) and then returns to the step 110 for waiting for the resending 
of the data. 
A second procedure for urging the participant to move to an adequate 
position is executed only by the terminal station 2, as follows. Every 
time the terminal station 2 sends the NAK signal to the hub station 1, it 
increments a counter d included in the memory 16 by 1. When the counter d 
reaches a preselected count, the terminal 2 displays an alarm on the 
operation/display section 11 thereof. 
In the second procedure, the participant carrying the terminal unit 2 moves 
to an adequate position in response to the alarm and then operates the 
operation/display section 11 for resetting the counter d. Of course, the 
controller 12 may automatically reset the counter d at the same time as it 
displays the alarm. In this procedure, the alarm may be implemented by an 
alert tone or vibration in place of or in combination with the display. 
Reference will be made to FIG. 4 for describing the operation of the 
control section 12 of the hub station 1 and that of the control section of 
the terminal station 2 particular to the second procedure. As shown, the 
control section 12 of the hub station 1 executes steps S202 through S204 
while the control section 12 of the terminal station 2 executes steps S205 
through S213. As for the hub station 1, the steps S102 through S109 shown 
in FIG. 3 also occur except for the omission of the steps 102 and S106 
through S109, and therefore steps S202 through S204 shown in FIG. 4 will 
not be described in order to avoid redundancy. 
As shown in FIG. 4, the control section 12 included in the terminal station 
2 rests the counter d for counting the NAK signals sent to the hub station 
1 (step S205). The control section 12 receives the data sent from the hub 
station 1 via the radio section 13 (step S206). The control section 12 
neglects the received data if the data is the resent data and if the 
terminal station 12 has already received the same data correctly. 
Subsequently, the control section 12 determines, based on the error 
checking code added to the received data, whether or not an error exists 
in the data (step S207). If the answer of the step S207 is Y, the control 
section 12 writes the received data in the MEM 15 of the terminal unit 2 
(step S208) and then returns to the step S206. 
If the answer of the step S207 is N, meaning that the received data 
includes an error, the control section 12 sends the NAK signal to the hub 
station 1 (step S209) and increments the counter d by 1 (step S210). Then, 
the control section 12 determines whether or not the counter d has 
exceeded the threshold TH (step S211). If the answer of the step S211 is 
N, the control section 12 returns to the step S206. If the answer of the 
step S211 is Y, the control section 12 displays an alarm on the 
operation/display section 11 (step S212), resets the counter d (step 
S213), and then returns to the step S206 for awaiting the resending of the 
data. 
In summary, in accordance with the present invention, a radio conference 
system gives an alarm to the participant of a conference either directly 
or via a chairman, urging the participant to move to a position of good 
wave propagation condition between a terminal station held by the 
participant and a hub station assigned to the chairman. This prevents the 
transmission efficiency of the entire system, possibly including many 
other terminal stations, from being lowered due to a remedy against the 
defective wave propagation to only a small number of terminal stations. 
Modifications of the invention herein disclosed will occur to a person 
skilled in the art and all such modifications are deemed to be within the 
scope of the invention as defined by the appended claims.