Abstract:
In a wireless communication system, mobile unit and base station access request and page transmissions are addressed by employing an efficient unified approach for the transmission and detection of both access requests from a mobile unit and pages from a base station. To this end, a mobile unit monitors for access requests and monitors a prescribed resource to detect if a page has been received. Upon detection of an access request, a corresponding request message is generated and transmitting substantially immediately to a base station, thereby minimizing latency in the access process. Concurrently, a base station monitors to determine if a page indication has been received and monitors a prescribed resource to determine if an access request message has been received. In this process, the processing of request messages takes precedence over the processing of pages. Upon detecting a received request message a request response message is generated and transmitted substantially immediately to the mobile unit, thereby also minimizing latency in the access process.

Description:
RELATED APPLICATION 
     U.S. patent application Ser. No. 09/596434 was filed concurrently herewith. 
    
    
     TECHNICAL FIELD 
     This invention relates to wireless communications systems and, more particularly, to wireless communications between mobile units and base stations. 
     BACKGROUND OF THE INVENTION 
     The basic mechanism in wireless communication systems for a base station and one or more mobile units to communicate is to exchange messages by utilizing a so-called segment. One such wireless system is the Orthogonal Frequency Division Multiplex (OFDM) system. A segment, as shown in FIG.  2  and further described below, is a combination of a time slot index and a waveform index. A time slot is a basic time unit having a unique time slot index associated with it. During any particular time slot interval there could be several waveforms that are transmitted and received that may or may not be orthogonal. Each waveform has a unique waveform index. Messages of particular interest in wireless communication systems are mobile unit requests on an uplink and base station pages on a downlink. 
     Typically, a mobile unit can tolerate delays in receiving a page message from a base station. However, a mobile unit when transmitting a request, must convey the request to the base station and receive a request response message as soon as possible to keep latency to a minimum. 
     SUMMARY OF THE INVENTION 
     Problems and limitations related to prior wireless communication system mobile unit and base station access request and page transmissions are addressed by employing an efficient unified approach for the transmission and detection of both access requests from a mobile unit and pages from a base station. 
     To this end, a mobile unit monitors for access requests and monitors a prescribed resource to detect if a page has been received. Upon detection of an access request, a corresponding request message is generated and transmitting substantially immediately to a base station, thereby minimizing latency in the access process. Concurrently, a base station monitors to determine if a page indication has been received and monitors a prescribed resource to determine if an access request message has been received. In this process, the processing of request messages takes precedence over the processing of pages. Upon detecting a received request message a request response message is generated and transmitted substantially immediately to the mobile unit, thereby also minimizing latency in the access process. 
     More specifically, the mobile unit monitors prespecified signal assignment (A) segments for page messages from a base station. Upon receiving a page message, the mobile unit transmits an appropriate acknowledgment message to the base station and then performs the action specified in the received page message. If an access request is received, a request message is generated and transmitted to the base station substantially immediately in a request (R) segment in a time slot dedicated to the particular mobile unit. Then, the mobile unit monitors all received A-segments for a request response message from the base station. Upon receiving the request response message an appropriate acknowledgment message is transmitted in an ACK-segment to the base station. Then, the mobile unit performs the action specified in the received request response message. The mobile unit simultaneously monitors for both the page messages and the access requests and the processing of access requests takes precedence over processing of received page messages. 
     In a base station, if a page indication is received an appropriate page message is transmitted in an assigned A-segment to the mobile unit. Upon receiving a corresponding acknowledgment message from the mobile unit, the base station performs the action specified in the page message. If an access request message is detected in assigned R-segments, the base station generates and transmits substantially immediately an appropriate request response message to the mobile unit. Then, upon receiving an appropriate acknowledgment message from the mobile unit, the base station performs the action specified in the received request message. The base station simultaneously monitors for both the request messages and the pages and processing of received access request messages takes precedence over processing of page indications. 
     Thus, applicants&#39; unique invention employs this unified technique to address both the page and access request processes that balances their divergent requirements. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 shows, in simplified block diagram form, details of a base station and a mobile unit in which the invention may be employed; 
     FIG. 2 is a graphical representation of a segment useful in describing the invention; 
     FIG. 3 is a graphical representation illustrating assignment of request (R) segments useful in describing the invention; 
     FIG. 4 is a graphical representation illustrating the transmission of pages useful in describing the invention; 
     FIG. 5 is a graphical representation illustrating the transmission of request response messages useful in describing the invention; 
     FIG. 6 is a graphical representation illustrating the transmission of acknowledgment segments useful in describing an aspect of the invention; 
     FIG. 7 is a graphical representation illustrating the process for monitoring assignments segments useful in describing the invention; 
     FIGS. 8A and 8B are high level flowcharts illustrating steps of processes employed in a base station and mobile unit in monitoring and transmitting request messages, respectively; 
     FIGS. 9A and 9B are high level flowcharts illustrating steps in processes employed in a mobile unit and a base station in monitoring and transmitting pages, respectively; 
     FIG. 10 is a graphical representation illustrating the high level logical flow for a mobile unit initiated request message; 
     FIG. 11 is a graphical representation illustrating the high level logical flow for a base station initiated paging message; 
     FIG. 12 is a state diagram illustrating steps in a unified process employed in a mobile unit for initiating request messages and monitoring paging messages in accordance with the invention; and 
     FIG. 13 is a state diagram illustrating steps in a unified process employed in a base station for initiating paging messages and monitoring request messages in accordance with the invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows, in simplified block diagram form, details of a base station and a mobile unit in which the invention may be employed. Specifically, shown are base station  101  and mobile unit  102 . It is noted that only a single mobile unit  102  is shown but, typically, a set including a number of mobile units, shares a base station  101 . In this example, base station  101  includes transmitter  103 , receiver  104  and controller  105  for transmitting and receiving wireless messages via antenna  106 . Controller  105  is employed to control operation of transmitter  103  and receiver  104 , in accordance with the invention. Similarly, in this example, mobile unit  102  includes transmitter  107 , receiver  108  and controller  109  for transmitting and receiving wireless messages via antenna  110 . Controller  109  is employed to control operation of transmitter  107  and receiver  108 , in accordance with the invention. 
     FIG. 2 is a graphical representation of a segment useful in describing the invention. As indicated above, the basic mechanism in wireless communication systems for a base station  101  and one or more mobile units  102  to communicate is to exchange messages by utilizing a so-called segment. A time slot is a basic time unit and associated with it is a unique time slot index. During any particular time slot there could be one or more waveforms that are transmitted or received. Each of the waveforms has a unique waveform index. A segment is defined as being a combination of a time slot index and waveform index. Base station  101  or mobile unit  102  transmits or receives messages by utilizing segments. The size of the time slot and specific waveforms carried therein could vary depending on the particular message, i.e., whether the message is a request (R), request response (RR), page (PG), or an acknowledgment (ACK). The waveforms carried in any particular time slot could be orthogonal, i.e., waveforms that do not interfere with one another. It is noted that the choice of orthogonal waveforms could reduce interference between mobile units transmitting in the same time slot. 
     FIG. 3 is a graphical representation illustrating assignment of request (R) segments useful in describing the invention. Each mobile unit  102  (FIG. 1) conveys request messages by transmitting them in a predetermined R-segment. To this end, each mobile unit  102  is assigned a sequence of recurring time slots, i.e., a dedicated uplink resource, during which requests can be transmitted. Thus, as shown in FIG. 3, mobile # 1  has access to an R-segment in the second time slot and, then, in the n th  time slot. In this example, mobile # 2  is also shown as having access to an R-segment in the second time slot. Indeed, several mobile units  102  can transmit requests simultaneously by using different waveforms. Typically, only a single mobile unit  102  uses a specific R-segment. This avoids the pitfalls of sending request messages by a random access scheme. It is also noted that the individual mobile units  102  can have different periodicities for the assigned R-segments. The R-segments represent the grant of dedicated uplink resources to mobile units  102  to convey their access requests to base station  101 . 
     FIG. 4 is a graphical representation illustrating the transmission of pages useful in describing the invention. Base station  101  can transmit a page to a mobile unit  102  in an assignment (A) segment. In order to reduce processing in a mobile unit  102  the page messages in A-segments may arrive only in a sequence of recurring A-segments. A mobile unit  102  therefore can monitor only prespecified A-segments, with base station  101  and the mobile unit  102  having an understanding regarding the prespecified A-segments. Thus, as shown in FIG. 4, regarding an A-segment destined for mobile unit # 2  both mobile unit # 1  and mobile unit # 2  are monitoring A-segments, and for an A-segment destined for mobile # 1  both Mobile unit # 1  and mobile unit # 3  are monitoring A-segments. 
     FIG. 5 is a graphical representation illustrating the transmission of request response messages useful in describing the invention. Base station  101  after detecting a request message from a mobile unit  102  transmits back a request response message in an A-segment. This response message includes the identification of the mobile unit  102  that the request response message is directed to. The mobile unit  102  is monitoring all A-segments received after it had transmitted the request message in order to detect the expected request response message from base station  101 . Thus, FIG. 5 shows that after transmitting a request message in an R-segment, a request response message can be received in any of the A-segments. 
     It is seen that the same A-segments can be used for transmitting both the request response messages and the page messages. This is possible because in many instances both the request response message and the page message lengths are similar. One example being when a request message conveys a request state migration and a request response message grants the state migration requested and the page message is an order by the base station  101  to the mobile unit  102  to migrate to a different state. In such instances both the page and request response messages can be accommodated in the same A-segment. To accommodate messages that are too large to fit in an A-segment, a pointer is placed in the A-segment to indicate the location where the mobile unit  102  can then look up and obtain the remainder of the message. When combining the page and request response messages into a single A-segment the associated type of message, i.e., whether it is a page or a request response message needs to be indicated. 
     FIG. 6 is a graphical representation illustrating the transmission of acknowledgment segments useful in describing an aspect of the invention. Note that for each assignment (A) segment there is a corresponding acknowledgment (ACK) segment. 
     An acknowledgment message is transmitted by a mobile unit  102  as follows: 
     (a) when a mobile unit  102  receives a page message; and 
     (b) when a mobile unit  102  receives a request response message that is consistent with the original request message. 
     The purpose of the acknowledgment message is: 
     (1) to provide a consistent state transition by both the base station  101  and the mobile unit  102 ; and 
     (2) to eliminate unnecessary state transitions by both the base station  101  and the mobile unit  102 , caused by false alarms or misdetections. 
     Acknowledgment messages could possibly be eliminated if the request messages were made very reliable. However, this would be extremely costly in terms of the time bandwidth resource, because the request segments are a dedicated resource for the mobile units, whereas the acknowledgment segments are a shared resource. On the otherhand, by making the acknowledgment messages very reliable savings are realized in system resources. 
     FIG. 7 is a graphical representation illustrating the process for monitoring assignments segments useful in describing the invention. Specifically, FIG. 7 shows the dynamic behavior of the mobile units  102 . A mobile unit  102  generally monitors only its assigned received A-segments for a page message, namely, A-segments  701  and  702 . After a mobile unit  102  transmits a request message, it monitors all received A-segments, namely,  704 ,  705 ,  706 , etc., for a request response message. In practice, a mobile unit  102  might time out after monitoring a predetermined number of A-segments. The logic being that the base station  101  is too busy to service its request. This would save processing power and, hence, extend the battery life of the mobile unit  102 . 
     FIGS. 8A and 8B are high level flowcharts illustrating steps of processes employed in a base station and mobile unit in monitoring and transmitting request messages, respectively. Thus, as shown in FIG. 8A, base station  101  in step  801  monitors request channels for incoming request messages and if a request is received from a mobile unit  102  step  802  causes a request response message to be transmitted. Thereafter control is returned to step  801  and steps  801  and  802  are iterated. As shown in FIG. 8B, a mobile unit  102  in step  803  waits for requests to be initiated, i.e., generated. Upon a request being generated, step  804  causes a request message to be transmitted in an R-segment assigned to the mobile unit  102 . Then, step  805  tests to determine if a request response message has been received from base station  101 . If the test result in step  805  is NO, control is returned to step  804  and steps  804  and  805  are iterated until step  805  yields a YES result. Upon step  805  yielding the YES result, step  806  causes the mobile unit  102  to migrate to a next state. 
     FIGS. 9A and 9B are high level flowcharts illustrating steps in processes employed in a mobile unit and a base station in monitoring and transmitting pages, respectively. Specifically, as shown in FIG. 9A, in step  901  mobile unit  102  monitors paging channels for pages from base station  101 . Upon receiving a page message from base station  101  in step  902 , step  903  causes mobile unit  102  to migrate to a next state. As shown in FIG. 9B, base station  101  in step  904  waits to obtain paging messages. 
     Upon receiving a paging message, step  905  causes base station  101  to transmit a page message including the identification of the corresponding mobile unit  102 . 
     FIG. 10 is a graphical representation illustrating the high level logical flow for a mobile unit  102  initiated request message. A mobile unit  102  transmits a request message in an R-segment conveying a request for a specific service from base station  101 . Upon receiving the request, base station  101  transmits a request response message in an appropriate assignment segment, i.e., A-segment. The mobile unit  102  upon receiving the request response message will transmit an acknowledgment message in a specific ACK-segment provided that the request response message satisfies prescribed correctness requirements. 
     FIG. 11 is a graphical representation illustrating the high level logical flow for a base station  101  initiated paging message. Base station  101  transmits a page message in an appropriate A-segment. A mobile unit  102  monitors the A-segments and upon receiving the page message transmits an acknowledgment message in a specific ACK-segment provided that the page message satisfies prescribed correctness requirements. 
     At the outset, it is felt best to define a number of state variables employed in the process illustrated in the flow chart of FIG. 12, and also in the process illustrated by the flowchart of FIG. 13, described below. The variables X and Y are maintained by the base station  101  and are used to set the appropriate fields in the page and request response messages. There are a significant number of different kinds of page and request messages and they can be thought as belonging to different classes. The page messages could be of “n” different classes and request messages could be of “m” different classes. DR and DP are internal state variables maintained by base station  101  and take on “m” and “n” values, respectively, to indicate the message class. Y indicates whether the message is a page or request response message and can be thought of as taking values P or R, respectively. X indicates the message class. The variables X and Y are functions of DP and DR. One specific function of particular interest is: after defining the priority or relative importance of all the (m+n) message classes the variables X and Y are defined as follows 
     X=max(DR, DP) 
     Y=P if DP&gt;DR 
     Y=R otherwise. 
     By way of an example, consider the situation of m=2 and n=3; let rc 1  and rc 2  be the message classes for request messages; let pc 1 , pc 2  and pc 3  be the message classes for page messages. Then, if the request and page messages have the following priorities 0&lt;rc 1 &lt;pc 1 &lt;rc 2 &lt;pc 2 &lt;pc 3 , the above functions for X and Y result in the following tables: 
     
       
         
               
               
             
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 DP 
               
             
          
           
               
                   
                 DR 
                 0 
                 pc1 
                 pc2 
                 pc3 
               
               
                   
                   
               
             
          
           
               
                 X 
               
             
          
           
               
                   
                 0 
                 0 
                 pc1 
                 pc2 
                 pc3 
               
               
                   
                 rc1 
                 rc1 
                 pc1 
                 pc2 
                 pc3 
               
               
                   
                 rc2 
                 rc2 
                 rc2 
                 pc2 
                 pc3 
               
             
          
           
               
                 Y 
               
             
          
           
               
                   
                 0 
                 0 
                 P 
                 P 
                 P 
               
               
                   
                 rc1 
                 R 
                 P 
                 P 
                 P 
               
               
                   
                 rc2 
                 R 
                 R 
                 P 
                 P 
               
               
                   
                   
               
             
          
         
       
     
     FIG. 12 is a state diagram illustrating steps in a unified process employed in a mobile unit  102  for initiating request messages and monitoring paging messages in accordance with the invention. In state  1201  the mobile unit  102  monitors for access requests and assigned A-segments for a received page, as shown in FIG.  7  and described above. Upon receiving a page, i.e., variable Y=P, state  1202  is entered and a corresponding ACK-segment including an appropriate acknowledgment message is transmitted to base station  101 . Thereafter, state  1204  causes mobile unit  102  to perform the action indicated in the received A-segment. Returning to state  1201 , if an access request is detected, i.e., variable Y=R, a request message is transmitted to base station  101  in an R-segment assigned to this particular mobile unit  102  and state  1203  is entered. In state  1203  mobile unit  102  is caused to monitor all A-segments for a request response message from base station  101 . If an appropriate request response message is not received in one of a prescribed number of A-segments, mobile unit  102  is caused to return to state  1201 . That is, mobile unit  102  has timed out and retransmission of the R-segment including the request message is terminated. When mobile unit  102  receives a request response message including [X,Y] it checks for its correctness. One example of a correctness definition is that [X,Y] is correct if Y=R and X is consistent with the original transmitted request message. If an appropriate request response message is not received, the R-segment is retransmitted in the assigned time slots until timing out of mobile unit  102  occurs. Upon a correct [X,Y] being received in state  1203 , mobile unit  102  enters state  1202  and an ACK-segment including an appropriate acknowledgment message is transmitted to base station  102 . Thereafter, state  1204  is entered and mobile unit  102  is causes to perform the action specified in the received A-segment. 
     FIG. 13 is a state diagram illustrating steps in a unified process employed in a base station  101  for initiating paging messages and monitoring request messages in accordance with the invention. In state  1301 , state variables DP and DR are set to zero ( 0 ). Then, in state  1302  base station  101  monitors for indications of paging messages and assigned R-segments for received request messages. If a page message is detected state  1303  sets DP to a “n” value to indicate the page message class. State  1305  causes base station  101  to transmit the page message in an assigned A-segment to mobile unit  102 . If in state  1305  a request message is received state  1304  is immediately entered. This is important to minimize any delay in providing access to a requesting mobile unit  102 . Returning to state  1305 , if no ACK-segment is received the page message is again transmitted in the assigned A-segment. If an ACK-segment is received including an appropriate acknowledgment message state  1306  is entered and base station  101  is caused to perform the action specified in the ACK-segment message. Returning to state  1302 , if a request message is received in an assigned R-segment, state  1304  is entered and state variable DR is set to a “m” value indicating its class. Then, state  1307  transmits a request response message in an A-segment as soon as possible. Again, this is to insure that any delay is minimized in providing access to a requesting mobile unit  102 . If no ACK-segment is received including an appropriate acknowledgment message state  1308  sets DR back to zero ( 0 ) and state  1302  is reentered. If an appropriate acknowledgment message is received in an ACK-segment, state  1306  causes base station  101  to perform the action specified in the request response message in the A-segment. 
     It should be noted that actions performed by mobile unit  102  and base station  101  in states  1204  and  1306 , respectively, are consistent. 
     The above-described embodiments are, of course, merely illustrative of the principles of the invention. Indeed, numerous other methods or apparatus may be devised by those skilled in the art without departing from the spirit and scope of the invention.