Abstract:
Bandwidth efficiency is increased by tailoring the use of ARQ transmission techniques to those situations where the signal quality on the mobile terminal uplink channel is expected to be poor. The signal quality on a downlink channel may be examined prior to uplinking a message from a mobile terminal to a base station. In response to the examination indicating that the signal quality on the uplink channel is below a predetermined threshold, the mobile terminal assumes an ARQ transmission mode, but if the examination indicates that the signal quality is not below the threshold, the mobile terminal assumes an non-ARQ transmission mode. Advantageously, the message length may also be used to help determine whether the ARQ transmission mode should be used.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to transmission methods utilized by wireless communications mobile terminals, such as cellular telephones, and more particularly to the use of automatic retransmission request transmission techniques.  
           [0002]    Wireless communications systems employ various techniques to handle erroneously received information. Generally speaking, these techniques include those which aid a receiver to correct the erroneously received information, e.g., forward error correction (FEC) techniques, and those which enable the erroneously received information to be retransmitted to the receiver, e.g., automatic retransmission request (ARQ) techniques. FEC techniques include, for example, convolutional or block coding of the data prior to modulation, where redundant information is added to the data to aid in the correction of certain errors. ARQ techniques involve analyzing received blocks of data for missing data and requesting retransmission of missing blocks. While these techniques aid in the accurate receipt of data, the use of such techniques necessarily consumes additional bandwidth. As such, it may be advantageous to limit the use of such techniques to situations where the benefit of the more robust transmission offsets the additional bandwidth consumed.  
         BRIEF SUMMARY OF THE INVENTION  
         [0003]    The present invention allows for more efficient use of bandwidth by tailoring the use of ARQ transmission techniques by wireless communications mobile terminals to those situations where the signal quality on the uplink channel is expected to be poor. The process includes examining the signal quality on a downlink channel when a message is to be uplinked from a mobile terminal to a base station. An ARQ transmission technique is selectively used to transmit the information on the uplink channel based on that examination of the downlink channel. For instance, in response to the examination indicating that the signal quality on the uplink channel is below a predetermined threshold, the mobile terminal assumes an ARQ transmission mode, but if the examination indicates that the signal quality is not below the threshold, the mobile terminal assumes an non-ARQ transmission mode. Advantageously, the message length may also be used to help determine whether the ARQ transmission mode should be used. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]    [0004]FIG. 1 shows a exemplary wireless communications system.  
         [0005]    [0005]FIG. 2 shows one exemplary process flow for the present invention.  
         [0006]    [0006]FIG. 3 shows another exemplary process flow for the present invention.  
         [0007]    [0007]FIG. 4 shows one exemplary functional block diagram of a mobile terminal. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0008]    Referring now to the drawings, FIG. 1 is a schematic representation of the radiocommunication environment in which a mobile terminal  20  operates. Mobile terminal  20  is in the coverage area of a public land mobile network (PLMN)  100 . PLMN  100  comprises one or more base stations  110 , each coupled to an antenna  112 . Each base station  110  provides radiocommunication services to mobile terminals  20  within its area of coverage, which is generally referred to as a cell. Each base station  110  connects to a mobile switching center (MSC)  102 , which in turn connects to the Public Switched Telephone Network (PSTN)  300 . The PLMN  100  may have more than one MSC  102  which interconnect to form a core network, as is well known in the art. Mobile terminal  20  and PLMN  100  may employ a wide variety of communication standards and protocols, which are published by organizations such as the Telecommunications Industry Association/Electronics Industry Association (TIA/EIA) and the European Telecommunication Standards Institute (ETSI), including without limitation Time Division Multiple Access (TDMA) standards such as TIA/EIA-136 and the Global System for Mobile Communications (GSM), Code Division Multiple Access (CDMA) standards such as TIA/EIA-95, Wideband Code Division Multiple Access (WCDMA) standards such as cdma2000, Universal Wireless Communications (UWC) 136, and satellite communication standards such those known as Globestar.  
         [0009]    The transmissions between the mobile terminal  20  and the base station  110  may be conceptually divided into the downlink channel  140  for transmissions from the base station  110  to the mobile terminal  20  and the uplink channel  160  for transmissions from the mobile terminal  20  to the base station  110 . While it is possible that the downlink channel  140  and the uplink channel  160  are merely different timeslots on the same physical frequency, this is not required and the downlink channel  140  may use one physical frequency and the uplink channel  160  another physical frequency.  
         [0010]    For uplink transmissions, the mobile terminal  20  may employ any one of a wide variety of transmission techniques well known in the art that do not employ an automatic retransmission request (ARQ) approach. For simplicity, these non-ARQ techniques may be referred to herein as “normal” transmission techniques. While normal transmission techniques are suitable for the majority of conditions, it is not uncommon for the signal quality on the uplink channel  160  to be relatively poor, possibly leading to missing data when normal transmission techniques are used. As such, many communications standards (protocols) include provisions for ARQ transmission techniques. For instance, the communications standard known as TIA/EIA-136, which is incorporated herein by reference, includes provisions for ARQ (see TIA/EIA-136-133-A). The general operation of the various types of ARQ transmission techniques are well known to those in the art.  
         [0011]    While TIA/EIA-136 and other standards allow for ARQ transmission techniques, the standards are believed to determine whether or not ARQ transmission techniques should be used based solely on whether the respective components (e.g., the mobile terminal  20  and the base station  110 ) are designed support the ARQ approach, and not based on the actual need for the ARQ approach based on signal conditions. In contrast, the present invention tailors the use of ARQ transmission techniques by mobile terminals  20  to those situations where the signal quality on the uplink channel  160  is expected to be poor, thereby using the more bandwidth efficient normal transmission techniques whenever possible.  
         [0012]    One process flow for transmitting information from the mobile terminal  20  to the base station  110  according to the present invention is shown in FIG. 2. When a message needs to be sent from the mobile terminal  20  to the base station  110  over a traffic channel (box  210 ), the mobile terminal  20  examines the signal quality of a downlink channel  140  (box  220 ) from the relevant base station  110 . The downlink channel  140  may advantageously be the downlink traffic channel  140  associated with the uplink traffic channel  160  that will be used, but this is not required. The examination of the signal quality of the downlink channel  140  (box  220 ) may include, for example, measuring the Bit Error Rate (BER) and/or the Received Signal Strength (RSSI) of the downlink channel  140 , or referencing recent measurements thereof. Continuing with BER and RSSI as representative examples, the BER of the downlink channel  140  is compared against a predetermined BER threshold value V BER  (box  230 ). A representative value of V BER  is three hundred. If the BER is not more than V BER  (box  230 ), then the mobile terminal  20  assumes a non-ARQ transmission mode (box  290 ) wherein the message is transmitted from the mobile terminal  20  to the base station  110  using a non-ARQ transmission mode. “Assuming” a mode in this context means that the mobile terminal  20  either changes to the desired mode or, if already in that mode, remains in the desired mode. If the BER is more than V BER  (box  230 ), then the RSSI is compared against a predetermined RSSI threshold V RSSI  (box  240 ). A representative value of V RSSI  is −111 dBm. If the RSSI not less than V RSSI  (box  240 ), then the mobile terminal  20  assumes a non-ARQ transmission mode (box  290 ) wherein the message is transmitted from the mobile terminal  20  to the base station  110  using a non-ARQ transmission technique. If the RSSI is less than V RSSI  (box  240 ), then the mobile terminal  20  assumes an ARQ transmission mode (box  250 ) wherein the message is transmitted from the mobile terminal  20  to the base station  110  using an ARQ transmission technique.  
         [0013]    Using the approach shown in FIG. 2, the ARQ transmission techniques are used to transmit the message from the mobile terminal  20  to the base station  110  when both the BER and the RSSI of the downlink channel  140  indicate that the signal quality of the uplink channel  160  is bad enough to warrant the use of ARQ. Otherwise, the normal transmission techniques are used. In this manner, the ARQ transmission techniques, and the accompanying consumption of bandwidth, are selectively used depending on the expected signal quality of uplink channel  160 .  
         [0014]    In the above example, both the BER and the RSSI of the downlink channel  140  were used as indicators of the expected signal quality of the uplink channel  160 . Of course, only one or the other need by used, but both may be advantageously used as a basis for determining whether ARQ or non-ARQ transmission techniques should be used. Also, other measures of signal quality on the downlink channel  140 , known to those of skill in the art, may be used instead or in addition thereto.  
         [0015]    The use of ARQ transmission techniques consumes additional bandwidth, as discussed above. As such, it may be advantageous to alter the process flow of FIG. 2 to include a qualifying pre-test prior to examining the signal quality on the downlink channel  140 . Such an approach is shown in FIG. 3. Much of the process of FIG. 3 is the same as in FIG. 2; however, prior to box  220 , the process of FIG. 3 checks the length of the message to be sent (box  215 ). If the message length is determined to be not longer than a predetermined length V LEN , such as forty bytes, the mobile terminal  20  assumes a non-ARQ transmission mode for the message (box  290 ) without examining the signal quality (box  220 ). On the other hand, if the message length is determined to be longer the predetermined length V LEN , the mobile terminal  20  proceeds to examine the downlink signal quality as in FIG. 2 (box  220 , etc.). As can be seen, the process of FIG. 3 limits the use of the selective ARQ application to relatively longer messages, accepting the risk of transmitting shorter messages with normal transmission techniques.  
         [0016]    As discussed above, the present invention may be advantageously employed in wireless communications mobile terminals  20 . One exemplary functional block diagram of a mobile terminal  20  is shown in FIG. 4. Mobile terminal  20  comprises a main control unit  22  for controlling the operation of the mobile terminal  20  and memory  24  for storing control programs and data used by the mobile terminal  20  during operation. Memory  24  may be contained in a removable smart card if desired. Input/output circuits  26  interface the control unit  22  with a keypad  28 , display  30 , audio processing circuits  32 , receiver  38 , transmitter  40 , and positioning receiver  50 . The keypad  28  allows the operator to dial numbers, enter commands, and select options. The display  30  allows the operator to see dialed digits, stored information, and call status information. The audio processing circuits  32  provide basic analog audio outputs to a speaker  34  and accept analog audio inputs from a microphone  36 . The receiver  38  and transmitter  40  receive and transmit signals using shared antenna  44 . The selective ARQ process of the present invention is typically carried out in the control unit  22  and/or by logic in the transmitter  40 .  
         [0017]    It should be noted that, as used herein, the term “mobile terminal”  20  may include a cellular radiotelephone with or without a multi-line display; a Personal Communications System (PCS) terminal that may combine a cellular radiotelephone with data processing, facsimile and data communications capabilities; a Personal Digital Assistant (PDA) may include a radiotelephone, pager, Internet/intranet access, Web browser, organizer, calendar and/or a global positioning system (GPS) receiver; and a conventional laptop and/or palmtop receiver or other appliance that includes a radiotelephone transceiver. Mobile terminals  20  may also be referred to as “pervasive computing” devices.  
         [0018]    The discussion above has assumed that the mobile terminal  20  is transmitting to a base station  110 , such as that shown in FIG. 1. However, it should be noted that “base station” is intended to refer to any portion of the PLMN  100  that stays in a relatively fixed position and communicates directly with mobile terminals. As such, “base station” should be broadly construed and is intended to include such components as “pico base stations,” radio heads, what is sometimes referred to as “BMI” (base station, MSC, and interworking function), and the like.  
         [0019]    The present invention may, of course, be carried out in other specific ways than those herein set forth without departing from the scope of the invention. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.