Abstract:
A method and monitoring station are disclosed that enable efficient communications between a monitoring station and a wireless device. The method includes determining that receipt of a first data packet by the monitoring station from the wireless device has been received without error, receiving a subsequent data packet at the monitoring station from the wireless device, determining that the subsequent data packet being received from the wireless device is a retransmission of the first data packet, and transmitting a first acknowledgement to the wireless device before the subsequent data packet is received in its entirety. A propagation delay may be estimated and used to adjust certain parameters of the monitoring station so as to account for excessive delays that are beyond the delays anticipated by and accommodated within the IEEE802.11 Standard.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is related to and claims priority to U.S. Provisional Patent Application Ser. No. 62/162,098, filed May 15, 2015, entitled SYSTEM AND METHOD FOR LONG RANGE WLAN COMMUNICATIONS, the entirety of which is incorporated herein by reference. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    n/a 
       FIELD 
       [0003]    The present disclosure relates to wireless communications and in particular to a method and monitoring station for enabling efficient long range communications between a monitoring and a target wireless device while overcoming range limitations due to timeout intervals. 
       BACKGROUND 
       [0004]    The present disclosure relates to communication between devices are based upon the IEEE 802.11 technology commonly known as Wi-Fi. IEEE Standard 802.11-2012 is used as the reference for the specifications used in this disclosure. The standard exchange of packets between two stations (STAs), such as between a STA A and STA B is for STA A to transmit a packet to STA B and then wait for the acknowledgment (ACK) packet to be received back from STA B before sending the next packet. In a standard infrastructure network, either STA A or STA B may be an access point (AP). Consider the case that STA A is an AP. After the AP has transmitted the packet to a STA, the AP will wait for a set timeout period that is dependent upon the channel frequency band and the physical data rate. If the ACK is not received within that timeout period, the AP will assume that the packet failed and will, in most cases, retry the transmission. In the case that successive transmissions of that packet do not receive an ACK within the specified timeout period, then the AP will retry the packet up to a retry limit and at that point discard the packet. If it is assumed that the packet was received error free at the STA, then as each packet is retried to the limit, the resultant throughput is a fraction of what it could be. 
         [0005]    The aforementioned timeout period is specified in the 802.11 Standard. The aforementioned timeout period is termed “ACKTimeout interval” and is defined as having a value as follows: 
         [0000]      ACKTimeout= a SIFSTime+ a SlotTime+ a PHY-RX-START-Delay. 
         [0006]    If the AP and the STA are co-operative then they can in fact, according to the Standard, adjust their ACKTimeouts to accommodate a known long range. This may be done by adding “aPropagationTime” to the “aSlotTime” in the formula above. In a fixed long range link, this may be done, i.e., the aSlotTime is extended, but for an unknown range this is impractical. In the case of the present disclosure, the AP does not know that the STA is far away and the STA is attempting to communicate at a distance. It is noted that the use of the term “long range communications” throughout this disclosure may be defined as a range such that the propagation time of the signals between the AP and the STA exceeds half the aACKTimeout value when the aSlotTime is not adjusted for air propagation time. 
         [0007]    The individual terms aSIFSTime, aSlotTime and aPHY-RX-START-Delay are specified in the 802.11 Standard for each physical layer (PHY). For example, for a Clause 16 Direct Sequence Spread Spectrum (DSSS) device, 1 and 2 Mbps in the 2.4 GHz band, Table 16.2 in the 802.11 Standard specifies aSIFSTime of 10 μs, aSlotTime of 20 μs and aPHY-RX-START-Delay of 192 μs. For a Clause 17 High Rate DSSS (HR/DSSS) device, 5.5 and 11 Mbps in the 2.4 GHz band, Table 17.5 in the 802.11 Standard specifies aSIFSTime of 10 μs, aSlotTime of 20 μs and aPHY-RX-START-Delay of “192 μs for long preamble and 96 μs for short preamble.” Each transmission starts with a preamble and header which is detected by the receiving device in order to correctly identify that the transmission is indeed an 802.11 conformant signal and subsequently correctly demodulate the packet. It should be noted that the aPHY-RX-START-Delay durations, for Clause 16 and 17 devices, commonly known as 802.11b, are equal to the preamble and header duration. Also, it should be noted that, in general, the long preamble is used when the packet is being transmitted at a PHY rate of 1 Mbps, and the short preamble is used when the packet is being transmitted at 2, 5.5 or 11 Mbps. 
         [0008]    When receiving a packet, the receiving Clause 16 or 17 device transmits the ACK after waiting a time period equal to aSIFSTime. If it is assumed that the distance between the AP and the STA, in the present example, is d feet, then the transmission from the AP will arrive at the STA after a delay of approximately d ns. The STA will wait aSIFSTime, e.g., 10 μs, and then transmit the ACK. The ACK transmission will also be delayed by d ns, and hence the AP will receive the ACK at a time (2d/1000+aSIFSTime) μs after the end of its packet transmission. Assuming that the packet transmitted by the AP is at 1 Mbps and hence uses the long preamble, the ACKTimeout interval will be equal to 10+20+192=222 μs which appears to allow for a value for d that equates to 212/2=106 μs, equal to a distance of about 20 miles. This however is not the case. The preamble and header duration is 192 μs and in theory this must be completed before the end of the ACKTimeout interval in order for the AP to know that a valid ACK packet is being received, and hence the start of the ACK must be received by the AP within only 20 μs after the end of its packet transmission. This would only allow a distance of less than 2 miles, which is not sufficient for long range communications. 
         [0009]    The preamble and header, for a long preamble, includes a 128 bit preamble, and a 16 bit start frame delimiter (SFD) followed by 48 header bits, a total of 192 bits, all sent at 1 Mbps. In practice, if the preamble is received within the ACKTimeout interval, then the AP may be able to recognize a valid signal and wait until the packet completes in order to establish that it is an ACK. In this case, the maximum delay would increase from 20 μs to (20+192−128)=84 μs, equivalent to a distance d of about 8 miles. Hence, in order that the ACK is received in time to prevent a retry, the maximum range of a 1 Mbps transmission, using a long preamble between the AP and STA, will be between 2 to 8 miles dependent upon the device specific implementation of the ACKTimeout interval. It should be noted that in the 802.11 Standard, 1 Mbps and 2 Mbps devices may detect the presence of a signal by implementing either an energy detect above a threshold, or by detecting a valid DSSS signal. The energy detect threshold is set at −80 dBm according to the 802.11 Standard but in general most 802.11b compliant devices use the valid signal detect, known as Carrier Sense (CS). Hence, it is necessary to detect the preamble bits and check that the valid DSSS code sequence is present. 
         [0010]    The above background description is based upon the Clause 16 and Clause 17 PHY layers of the 802.11 Standard. A similar situation is present for other PHY layers. If using the 2.4 GHz band, then it is also possible to use the orthogonal frequency division modulation (OFDM) of Clause 19 Extended Rate PHY (ERP), commonly referred to as 11g. Similarly, in the 5 GHz band, Clause 18 devices, commonly referred to as 11a, and Clause 20 devices, commonly referred to as 11n, use OFDM. In the cases when OFDM is in use, the lowest PHY rate, and hence the PHY rate most likely to be used for long distance communication, is at 6 Mbps. For 6 Mbps OFDM, the value for aSIFSTime, according to Table 19.8 of the 802.11 Standard, is 10 μs but a signal extension of 6 μs is specified which causes the effective value for aSIFSTime to be 16 μs which will be used for the purposes of the background discussion related to this disclosure. The aSlotTime, according to Table 19.8 of the 802.11 Standard is specified as either 20 μs or 9 μs, but in practice for OFDM the 9 μs slot time is used. The aPHY-RX-START-Delay is also specified in Table 19.8 of the 802.11 Standard and a value of 24 μs is given for OFDM. Hence, for a 6 Mbps OFDM packet, the ACKTimeout interval is 16+9+25=50 μs. The duration of the OFDM header is 20 μs. An OFDM device is required to detect the presence of a signal and set a trigger, using both energy detect, i.e., any energy detected above a set threshold, and carrier detect, i.e., the receipt of a valid header which will be at the receive sensitivity level. The returning ACK to a transmitted packet must therefore be detected within 9+25=34 μs. The signal detect is specified as being set within 4 μs of the start of the reception, according to 19.4.7 of the 802.11 Standard, hence the maximum delay due to range will be (34−4)/2=15 μs, or about 2.8 miles. Similar parameters apply to devices under Clause 18 of the 802.11 Standard, commonly known as 11a and devices under Clause 20 of the 802.11 Standard, commonly known as 11n. 
         [0011]      FIG. 1  is a block diagram of a standard communications link  100  between an AP  101  and a STA  105  in a typical IEEE 802.11 infrastructure network. The AP  101  has an antenna  102 . STA  105  has an antenna  106 . The distance between the two antennas is d  110 . The propagation time for a radio signal between the two antennas  102  and  103  will be d/C where C is the speed of light. If d is in feet, then the propagation time is about d ns. Assuming that a radio signal is transmitted by the AP  101 , if the distance  110  between the two antennas  102  and  106  is 1 mile, the radio signal received at antenna  106  will be delayed by 5.28 μs, referred to the time of the transmission from antenna  102 . 
         [0012]      FIG. 2  is a timing diagram that depicts the typical transmission of a packet from an AP  200  to a STA  205  in time. At time T 1   211 , the AP  200  starts to transmit packet  202 . Packet  202  has a duration of tp  230 . At time T 2   221  the STA  205  starts to receive the packet  203  which may or may not be identical to the transmitted packet  202  dependent upon the propagation conditions. For the purposes of this description it is assumed that packet  203  has the same content as packet  202 . At time T 3   212 , AP  200  completes the transmission of packet  202  and at time T 4   222 , STA  205  will complete receiving the packet  203 . The time differences (T 2 −T 1 ) and (T 4 −T 3 ) will be the same and will have a value δ  231  that corresponds to the distance between the AP  200  and the STA  205 , as previously described in  FIG. 1 . At time T 5   223 , STA  205  will transmit an acknowledgement packet (ACK)  221  back to the AP  200 . The time difference (T 5 −T 4 ), t SIFS    632 , will be equal to the aSIFSTime as defined in the 802.11 Standard which, as previously explained, is the time that a STA will wait after the completion of a received packet before sending an ACK packet in response. At time T 6   213  the ACK packet  222 , which is the same as the ACK packet  221  transmitted by the STA  205  at time T 5   223 , will start to be received by the AP  200 . Note that the time difference δ  233 , between T 6   213  and T 5   223 , will again represent the propagation time between the AP  200  and the STA  205  and will be equal in value to δ  231 . Hence, the time that elapses, at the AP  200 , from the end of the transmission T 3   212  of packet  202  to the start of the reception of the ACK packet  222  at time T 6   213  is equal to (2δ+aSIFSTime), where δ is the propagation time related to the distance between the AP  200  and the STA  205  as previously described in  FIG. 1 . As previously described, if the distance, and hence the propagation time, exceeds a certain value, then the AP  200  will receive the ACK  222  too late and it will assume that the transmitted packet  202  failed. At this point the AP  200  will start proceedings to send a retry of packet  202 . 
         [0013]      FIGS. 3 a  and 3 b    show the format of typical 802.11 data packets.  FIG. 3 a    is a diagram that shows the format  300  of an 802.11 transmitted packet using a long preamble at 2.4 GHz. The preamble  307  consists of a synchronization field  301  followed by the Start Frame Delineator (SFD)  302 . The synchronization field  301  consists of 128 bits in the case of the long preamble. The preamble  307  is followed by the header  308  which includes the signal, service, and length fields  303  followed by a cyclic redundancy check (CRC)  304 . Together the preamble  307  and header  308  comprise 192 bits and are sent at 1 Mbps. Hence the duration of the preamble and header is 192 μs. After the CRC 304 comes the media access control (MAC) header  305  and frame body  316 . At the end of the packet if the frame check sum (FCS)  309  which is used to check if the packet has been received with no errors. Referring back to  FIG. 2 , the time T 4   222 , the end of the received packet  203 , is the point at which the FCS error check has been carried out successfully. 
         [0014]      FIG. 3 b    is a diagram that shows the typical format  310  of an 802.11 transmitted packet using a short preamble at 2.4 GHz. This is similar to  FIG. 3 a    except that the synchronization field  311  of the preamble  317  is 56 bits compared to 128 bits for the synchronization field  301  used in the long preamble  307 . The synchronization field  311  is followed by the Start Frame Delineator (SFD)  312 . The preamble  317  is flowed by the header  318  which consists of the signal, service, and length fields  313  followed by a cyclic redundancy check (CRC)  314 . Together the preamble  317  and header  318  comprise 72 bits and are sent at 1 Mbps. Hence the duration of the preamble and header is 72 μs. The CRC 304 is followed by the MAC header  315  and frame body  316 . At the end of the packet is the frame check sum (FCS)  317 . In the case of a short preamble, the header  318  is transmitted at 2 Mbps. Hence, the short preamble can only be used if the MAC header  315  and packet frame body  316  is being sent at 2, 5.5 or 11 Mbps. For a 1 Mbps transmission, the long preamble  307   FIG. 3 a    is used. 
         [0015]      FIG. 4  is a block diagram that shows the typical format of an 802.11 OFDM transmitted packet  400  for clause 18, 19 and 20 devices of the 802.11 Standard commonly known as 11a, 11g and 11n respectively. The preamble and signal  407  are transmitted at the 6 Mbps OFDM rate. The preamble  401  is 16 μs in duration and includes 12 symbols, 10 short and 2 long. The preamble  401  is followed by the signal field  402  which is a single symbol. After the preamble and signal  407  comes the service and MAC frame  408  comprised of the service field  403 , the MAC header  404  the frame body  405  and finally the FCS  406 . The service and MAC frame  408  is transmitted at the chosen data rate for the packet. The preamble and signal  407  are sent at 6 Mbps. 
         [0016]    The FCS field is used to verify that the packet has been received correctly. If in a received packet the FCS check is correct then the ACK should be sent. If the FCS check fails then an ACK is not sent. Therefore, the point at which a device knows that a packet has been received, and that it is correct, is at the end of the packet after checking the FCS field. Also, it should be noted that the ACK packet is not transmitted until a time of aSIFSTime has elapsed after the end of the received packet. This is to allow time for the transmitting device to switch from transmit mode to receive mode in order to receive the ACK. When the AP and the STA are close, then the aSIFSTime is the elapsed time between the end of the transmitted packet and the start of the received ACK packet. If the AP and the STA are at a distance from each other, then the time between the end of the transmitted packet and the start of reception of the received ACK packet will be greater. Hence, the ACKTimeout interval is used to allow the transmitting station to wait for the ACK but not wait too long in the case that the ACK is not being sent. This restriction on the ACKTimeout interval is a limitation on efficient communications over extended ranges. 
         [0017]      FIG. 5  and  FIG. 6  describe a known method for estimating the time delay and hence the distance between two stations. The method described does not in itself form part of this disclosure, but the use of the method of measuring the delay and then using the result of the measurement to improve the communication at extended range does form part of this disclosure. 
         [0018]      FIG. 5  is a timing diagram that describes a basic active ranging method that may be used to determine the distance between a STA A  500  and another STA B  505 . The time axis  510  refers to STA A  500  and the time axis  520  refers to STA B  505 . At time T 1   511 , STA A  500  transmits a packet to STA B  505 . This transmission  512  is received at STA B  505  at time T 2   513 . The propagation time of the transmission  512  is (T 2 −T 1 )  530 . STA B  505  transmits a response  524  at time T 3   523 . The time  522  that has elapsed between the reception of the packet at time T 2   513  and the transmission at time T 3   523  is the turnaround time at STA B  505 . Ideally the turnaround time  522  at STA B will be equal in duration to aSIFSTime (SIFS). This is the case when the first transmitted packet is a ready-to-send (RTS) control packet which will generate a clear-to-send (CTS) control response packet. Also the initial packet may be a data null packet and the response an ACK packet. A variety of packets may be used. However, the turnaround time for the response packet should be known. At time T 4   514 , STA A  500  receives the response  524  from STA B  505 . The propagation time of the transmission  524  is (T 4 −T 3 )  534 . It should be noted that the time differences  530  and  534  represent the propagation time, δ, of the transmissions and should be equal assuming the distance between the two stations has not changed. The total time that elapses between the transmission  512  and the reception  524  at STA A  500  is: 
         [0000]      ( T 2− T 1)+( T 3− T 2)+( T 4− T 3)=( T 4− T 1)=δ+SIFS+δ  (5)
 
         [0000]      Hence, δ=( T 4− T 1−SIFS)/2  (6)
 
         [0019]    Expression (6) is a simplified equation that is included so as to provide an understanding of the general idea of a ranging transmission method. Note that the duration of the transmitted packet and the response packet is not accounted for in equation (5). Note also that, in practice, it is common that the timestamp of a packet is set to coincide with the end of the packet at the point where the FCS check is completed. 
         [0020]      FIG. 6  is a time diagram that describes in further detail a general ranging transmission method. Time axis  610  refers to STA A  600  and time axis  620  refers to STA B  605 . At time Ta  611  STA A starts the transmission of packet  602  which is addressed to STA B  605 . After a time delay of δ, at time Tb  621 , STA B  605  starts to receive packet  603 , which ideally is identical to packet  602 . Packet  603  may differ in the value of particular bits dues to propagation conditions but in general, the packets are the same. At time Tc  612  STA A  600  completes the transmission of packet  602  and at time Td  622  STA B  605  completes the reception of packet  603 . The time difference between Tc  612  and Td  622  is δ the propagation time for the packet to travel from STA A  600  to STA B  605 . Note that the time differences (Tc−Ta) and (Td−Tb) are both the duration tp  630  of the transmitted packet  602 . 
         [0021]    STA B  605  transmits the response packet  621  at time Te  623 . Assuming that the response is an ACK or an RTS packet in reply to the received packet  603 , time Te ideally will be at a time t SIFS    632  after time Td  622 , where t SIFS    632  is the aSIFSTime as defined in the IEEE 802.11 standard [1]. At time Tf  613 , STA A  600  starts to receive the response  622  which ideally is identical to response  621  sent by STA B  605 . At time Tg  624  STA B  605  completes the transmission of the response  621  and at time Th  622 , STA A  600  completes receiving the response  622 . Note that the time differences (Tb−Ta), (Td−Tc), (Tf−Te) and (Th−Tg) are all equal and have the value δ which is the propagation time for the packet and response to travel between the two STAs. At STA A  600 , the time of a packet at the point when the frame check has completed may be recorded. Hence, at STA A  600 , the monitoring station, the time for the transmission of packet  602  that is recorded is Tc  612 , and the time that is recorded for the reception of the response  622  is Th  614 . In order to calculate the value of δ it is necessary to know the duration tr  634  of the response  622 . Calculating the duration tr  634  is possible as the monitoring station, STA A  600  can monitor the details of the response packet such as data rate and length. In practice therefore, STA A  600  can calculate the value of δ from expression (7): 
         [0000]      δ=( Th−Td−tr−t   SIFS )/2  (7)
 
         [0022]      FIG. 7  is a diagram that shows the times associated with the sending of an 802.11 packet  700  using conventional timing and is drawn in more detail than that described in  FIG. 2  so as to include the details described in  FIG. 3  and  FIG. 4 . The packet  700  is transmitted by the AP  750  at time T 1   740 . At time T 2   741  the STA  760  starts to receive packet  710  which for is assumed to be identical to packet  700 . Also, for this example, the packet is a 1000 byte packet being transmitted at 1 Mbps on a 2.4 GHz channel. Time difference (T 2 −T 1 ) is the propagation delay. The transmitted packet  700  starts with the preamble field  701 , followed by the header field  702 , the MAC header  702 , the frame body  704  and finally the FCS field  705 . At time T 3   742  the AP  750  completes the transmission of the packet  700 . At the STA  760 , the reception of packet  710  is after the completion of the FCS at time T 4 . Time difference (T 4 −T 3 ) is the propagation delay, equal to (T 2 −T 1 ). At time T 5 , the ACK packet  720  is transmitted to the AP  750  by the STA  760 . The time difference (T 5 −T 4 ) may be equal to aSIFSTime or may be less, as previously described. At time T 6   745  the AP  750  starts to receive the ACK packet  730  which for purposes herein is identical to ACK packet  720 . Time difference (T 6 −T 5 ) is the propagation delay, equal to (T 2 −T 1 ) and (T 4 −T 3 ). At time T 7  the receipt of the preamble  731  of the ACK packet  730 , is completed. 
         [0023]    The time difference (T 7 −T 3 ) represents the time that has elapsed at the AP  750  after having completed the transmission of packet  700  and receiving, or identifying the receipt of the expected ACK packet. To illustrate the timing, the following example is used. For example, assuming a distance between the AP  750  and the STA  760  of 19 miles, the corresponding propagation delay is about 100 μs. A 1000 byte packet at 1 Mbps is 9130 μs duration in total. The duration of a 1 Mbps ACK packet is 304 μs of which the preamble is 128 μs duration. Continuing the example, assuming that aSIFSTime was used by the STA, then the delay (T 7 −T 3 ) has a value of 100+10+100+128=338 μs. This exceeds the ACKTimeout interval of 222 μs and therefore the AP  750  will have assumed that the packet  700  was not received and will proceed to retry the packet. There is every chance that the AP  750  will already be re-transmitting the packet  700  when the ACK is present at the AP antenna, but even if the ACK is received at this late time, the AP  700  will not know the source and will disregard it. It should be noted that ACK packets do not include the address of the originating station. ACK packets only include the destination address. 
         [0024]    In the case that a STA is attempting to establish long range communication with a standard AP such that it can receive from and transmit to that AP, the ACKTimeout interval used by the AP is assumed to be to the 802.11 Standard. However, when attempting long range Wi-Fi communications, associated propagation losses result in retries and degrades the communication throughput. Also, a timeout of the device waiting for the ACK may occur. One attempted solution is to increase the ACKTimeout interval, but this requires that the device is a special implementation. 
       SUMMARY 
       [0025]    The present disclosure advantageously provides a method and monitoring station for facilitating communications such as long range communications between a monitoring station and a wireless device. 
         [0026]    In one aspect of the disclosure, a method for communications between a monitoring station and a wireless device is provided. The method includes determining that receipt of a first data packet at the monitoring station from the wireless device has been received without error, receiving a subsequent data packet at the monitoring station from the wireless device, determining that the subsequent data packet being received from the wireless device is a retransmission of the first data packet, and transmitting a first acknowledgement to the wireless device before the subsequent data packet is received in its entirety. 
         [0027]    In another aspect of the disclosure, a method for communications between a monitoring station and a wireless device is provided where the method includes determining that receipt of a first data packet at the monitoring station from the wireless device has been received without error, receiving a subsequent data packet at the monitoring station from the wireless device, determining that the subsequent data packet being received from the wireless device is a retransmission of the first data packet by checking a MAC header of the received first data packet, determining a time of reception of a field of the subsequent data packet, determining a trigger time based on the determined time of reception of the field of the subsequent data packet, determining a time interval before transmitting a first acknowledgement, the time interval based upon the trigger time, and transmitting the first acknowledgement to the wireless device after the time interval has elapsed and before the subsequent data packet is received in its entirety. 
         [0028]    In accordance with still another aspect, the disclosure provides a monitoring station for long range communications with a wireless device. The monitoring station includes an interface configured to receive a first data packet from the wireless device, and receive a subsequent data packet at the monitoring station from the wireless device, and processing circuitry. The processing circuitry includes a processor, and a memory storing instructions that, when executed, configure the processor to determine that receipt of the first data packet from the wireless device has been received without error and determine that the subsequent data packet being received from the wireless device is a retransmission of the first data packet. The interface is further configured to transmit a first acknowledgement to the wireless device before the subsequent data packet is received in its entirety. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]    A more complete understanding of the present invention, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: 
           [0030]      FIG. 1  is a block diagram of a typical communications link between an AP and a STA in a typical IEEE 802.11 infrastructure network; 
           [0031]      FIG. 2  is a timing diagram that depicts the transmission of a packet from an AP to a STA; 
           [0032]      FIG. 3 a    is a block diagram that shows the format of an 802.11 transmitted packet using long preamble at 2.4 GHz; 
           [0033]      FIG. 3 b    is a block diagram that shows the format of an 802.11 transmitted packet using short preamble at 2.4 GHz; 
           [0034]      FIG. 4  is a block diagram that shows the format of an 802.11 OFDM transmitted packet; 
           [0035]      FIG. 5  is a timing diagram that shows the sequence of an exchange of 802.11 packets; 
           [0036]      FIG. 6  is an alternative timing diagram of the packet exchange shown in  FIG. 5 ; 
           [0037]      FIG. 7  is a diagram that shows the times associated with the sending of an 802.11 packet using conventional timing; 
           [0038]      FIG. 8  is a diagram that shows the times associated with the sending of an 802.11 packet using timing according to an embodiment of the present disclosure; 
           [0039]      FIG. 9  is a flow diagram illustrating the sending of a packet from one STA to a distant legacy STA or AP according to an embodiment of the present disclosure; 
           [0040]      FIG. 10  is a flow diagram illustrating the reception of packets from a distant legacy STA according to an embodiment of the present disclosure; 
           [0041]      FIG. 11  is a flow diagram illustrating the sending and reception of data packets and the estimation of the propagation delay by a monitoring station according to an embodiment of the present disclosure; 
           [0042]      FIG. 12  is a block diagram of a wireless communications device according to an embodiment of the present disclosure; and 
           [0043]      FIG. 13  is a flow diagram illustrating an exemplary process performed by a wireless communications device according to an embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0044]    This disclosure is for communication over extended ranges with devices that are based upon the IEEE 802.11 technology, commonly known as Wi-Fi. This disclosure is for the case of extended range communication from a monitoring device to a legacy target device. The legacy target device is one that complies with the 802.11 Standard, generally known as Wi-Fi, in that it is not modified in any way for extended range communications. The monitoring device is one that generally complies with the 802.11 Standard but has been modified, as described in this disclosure, so as to enable extended range communications with the target device. Although the embodiments disclosed herein relate to Wi-Fi communications, the disclosure is not limited to only Wi-Fi communications, and may be applied to other types of communications between wireless devices. 
         [0045]    Methods to overcome the range limit imposed by the ACKTimeout interval are described in this disclosure. Also, methods are disclosed that enable the monitoring Wi-Fi device to communicate at extended ranges with a legacy target Wi-Fi device. The legacy target device may be a device such as a station (STA) or an access point (AP). In the following description, the target legacy device is described as an AP as this represents a particular use case and aids in the descriptive process. However, the disclosure is not limited solely to such an arrangement. 
         [0046]    As discussed above, in compliance with the 802.11 Standard, the ACK packet is not transmitted until a time of aSIFSTime has elapsed after the reception of a data packet. However, according to embodiments disclosed herein, when at extended range, the ACK may be sent as quickly as possible after confirmation that the received packet is correct and hence effectively reduce the delay of the ACK being received and as such, increase the communication range. As also described herein, in another embodiment, the range, and hence the time delay between the devices is established, and then used as the basis for calculating the time that an ACK needs to be sent in order to be received in a timely manner and prevent retries. The procedure includes first receiving the packet and checking a field of the received packet, for example, the FCS field, and then, if the packet was received without error, sending an ACK to the retry of that packet, the ACK being sent before the retry packet has been received in its entirety. 
         [0047]    As previously explained, the ACK packet is not transmitted until a time of aSIFSTime has elapsed. The value of the aSIFSTime allows a minimum time for the transmitting device to switch from transmit mode to receive mode in order to receive the ACK. When at extended range, however, there is no need to wait for the full aSIFSTime and the ACK can be sent as quickly as possible after confirmation that the received packet is correct. For example, for an 802.11b compliant communication, if the ACK was sent 2 μs after the completion of the received packet, instead of waiting for 10 μs as required, then this would result in an effective increase of range of about 0.75 miles. In the case of an OFDM communication, where the aSIFSTime is 16 μs, a reduction of 14 μs in the delay in sending the ACK would result in a range increase of 1.32 miles. 
         [0048]    In one embodiment, the range between the devices and hence the time delay is determined, and then used as the basis for calculating the time that an ACK need to be sent in order to be received correctly and prevent retries. At extended ranges, the ACK to be sent by the monitoring STA in response to a packet being received from the target AP should be sent by the monitoring STA before the packet being received has completed, i.e., before the FCS check has been carried out. In addition, only a packet that has been received without errors should be acknowledged. Hence, in one embodiment, the packet is received and the FCS field checked, and then, if the packet was received without error, an ACK is sent to the retry of that packet, the ACK being sent before the retry packet has been received in its entirety. In order to calculate the time when the ACK needs to be sent such that it is received in time at the target AP, the monitoring STA uses the time delay previously established, to establish that the packet being received is indeed the expected retry packet, and then uses a timing trigger which needs to be based upon a reliable time point within the initial portion of the received packet. 
         [0049]      FIG. 8  is a diagram that shows the times associated with the transmission of an 802.11 packet  800  and the response according to an embodiment of this disclosure. The packet  800  is transmitted by the AP  850  at time T 1   840 . At time T 2   841  the STA  860  starts to receive packet  810  which shall be considered to be identical to packet  800 . Also, for this example, the packet is a 1000 byte packet being transmitted at 1 Mbps on a 2.4 GHz channel. Time difference (T 2 −T 1 ) is the propagation delay. The transmitted packet  800  starts with the preamble field  801 , followed by the header field  802 , the MAC header  803 , the frame body  804  and finally the FCS field  805 . At time T 3   842  the STA  860  receives the end of the preamble  811  and at time T 5   843  the STA  860  receives the end of the header field  812 . At time T 4   844  the STA  860  receives the end of the MAC header field  813 . As discussed above with respect to  FIGS. 3 a  and 3 b   , at the end of the header field there is a CRC check and hence the validity of the signal, service and length fields can be verified. At the end of the MAC header field  813 , the STA  860  can verify that the address fields present in the MAC header indicate that the packet originated from AP  850  and is addressed to STA  860 . The STA  860  can examine the sequence number of the packet, also in the MAC header, and furthermore, the STA  860  can verify that the packet is a retry by examining the retry bit in the frame control field of the MAC header. The address fields, sequence number and retry bit details can be seen by reference to  FIG. 8-1  MAC Frame Format and  FIG. 8-2  Frame Control Field in the 802.11 Standard, incorporated by reference herein. 
         [0050]    In one embodiment, it is desired that a packet is received without error. Referring back to  FIG. 7 , assume that this represents the case of the first attempt by the AP  750  to transmit a packet,  700 . In our example, the AP  750  assumes that the packet failed because it did not receive the ACK  730  in time. However, in the example shown in  FIG. 7 , STA  760  did receive the packet without error because an ACK was transmitted. Therefore, assume that  FIG. 8  represents the case where the AP  850  is sending the retry packet and that the STA  860  has already received that packet without error. Hence, at time T 5   844 , the STA  860  knows that the received packet is addressed to itself, it is a retry, and that the sequence number indicates that this is the same packet that it has previously received without error. In this case, STA  860  need not receive the rest of the packet  810 . Assume also that the packet delay (T 2 −T 1 ) has already been estimated as described with reference to  FIG. 5  and  FIG. 6 . Therefore at time T 5   844 , STA  860  can drop the reception of the packet  810  and prepare for the transmission of the ACK packet  820  at time T 6   845 . At time T 6   845 , STA  860  transmits the ACK packet  820 . At time T 7   846 , the AP  850  completes the transmission of the retry packet  800 . Because STA  860  has already started to send the ACK packet  820  at time T 6   845 , the ACK packet  830  is received at time T 8   847  at a time that is calculated by STA  860 , such that (T 8 −T 7 ) is between aSIFSTime and aSIFSTime plus aSlotTime. Thus, the AP  850  experiences the reception of a timely ACK  830  to its transmitted retry packet  800  and hence the AP  850  will note the successful transmission. 
         [0051]    A method used by STA  860  to calculate the time to start sending the ACK  820  is described using the same example described with reference to  FIG. 7 . In this example, it is still assumed that the distance between the AP  850  and the STA  860  is 19 miles, which corresponds to a propagation delay of about 100 μs. Packet  800  is a 1000 byte packet at 1 Mbps which has a duration of 9130 μs duration in total. The preamble and header is 192 μs, the MAC header is generally 26 octets which is 208 μs in duration. All of these values are known by the STA  860 . It should be noted that, even in the case where the retry packet is transmitted using a different data rate than the first packet, the information provided in the preamble and header field provide the information to calculate the duration of the packet. In our example, T 2   841  is 100 μs after the start of the packet  800  transmission at T 1   840 . Time T 5   844  will be 192+208=400 μs after time T 2   841 . At time T 5   844  STA  860  has verified that this is indeed the desired retry packet. STA  860  knows that the packet  800  will finish transmission at time T 7   846  which is 9130−100−400=8630 μs after STA  860  has verified the end of the MAC header  813  at time T 5 . STA  860  also knows that there will be a delay of 100 μs for the ACK packet  820  to reach the AP  850  so hence, STA  860  will start to send the ACK packet  820  at time T 6   845  where (T 6 −T 5 )=9130−100−400−100+10=8540 μs. Therefore, the following times correspond to  FIG. 8 : T 1 =0, T 2 =100 μs, T 5 =500 μs, T 6 =9040 μs, T 7 =9130 μs and T 8 =9149 μs. Hence, the ACK packet  830  arrives at AP  850  10 μs after the end of packet  800 , a time equal to aSIFSTime. It should be noted that the time for the STA  860  to generate the ACK  820  to a retry packet  800  can be readily calculated so as to arrive at the AP  850  at the correct time. Although some implementations of devices have been observed to not use an accurate aSIFSTime, a variation of a few microseconds will not cause the generated ACK to arrive too late. Indeed, it might be prudent to base the calculation on aSIFSTime plus a few microseconds, for example, 5 μs, to cover the case where a device may be using an incorrect aSIFSTime. 
         [0052]      FIG. 9  is a flow chart that describes an embodiment of the disclosure when transmitting packets from the monitor STA  860  to the target STA or AP  850 . The process  900  may start at block  901  and may be followed by block  902  which carries out the ranging process as described in  FIG. 5  and  FIG. 6 . Note that although specific distances are used in the examples, this is for ease of explanation. Implementations are not limited to the distances described. Block  902  may be repeated at set intervals or as required. After block  902 , block  903  may repeat the ranging process of block  902 , as required. The ranging process may be repeated periodically according, for example, to the relative movement between the stations due to, for example, the velocity of the platform upon which the monitoring STA  860  is located. An alternative method to the ranging process described in  FIG. 5  and  FIG. 6  is that if a location is otherwise established or known for the target station, such as GPS co-ordinates, then with knowledge of the location of the monitoring STA  860  the distance to the target and hence the delay can be calculated. Block  902  may be followed by block  904  where the packet is transmitted. After transmission in block  904 , the STA  860  will wait for an ACK from the target. The expected wait time before the ACK is received will be the delay time, which may be as determined in block  902 , plus aSIFSTime. This wait time may be in excess of the standard ACKTimeout interval and therefore the monitor STA  860  may use a value for ACKTimeout interval that is equal to the delay plus the ACKTimeout interval. 
         [0053]    To accommodate extended ranges, the ACKTimeout interval may need to be increased and this increased value is used in block  905 . In block  906  it is determined if the ACK is received. If no ACK is received within the adjusted ACKTimeout interval, the packet may be retried via block  908  by returning to block  904 . If the ACK is received successfully in block  906 , then the next packet is transmitted in block  907 , and in block  909  it is determined if there is another packet being transmitted. If another packet is to be transmitted, the next packet may be transmitted via block  904 . If there is not another packet to be transmitted, as checked in block  909 , the process may return to block  902  or may simply wait for another packet to be transmitted in block  904 . The decision to carry out another ranging measurement in block  902  may be determined by block  910 . 
         [0054]      FIG. 10  is a flow diagram  1000  of an embodiment of this disclosure showing the blocks to receive packets at a monitoring STA  860  from a distant legacy STA or AP.  850  The process herein described is comparable with the descriptions provided for  FIG. 7  and  FIG. 8 . The process may begin with block  1001 . Within block  1001 , the one way propagation delay σ, which may be determined as described above and in  FIG. 5  and  FIG. 6 , as per block  902  of  FIG. 9 , will be known. After initialization in block  1001 , the reception of a packet may be detected in block  1002 . Block  1002  represents the reception for the first time of a particular packet. If the packet is received in block  1002 , the packet is demodulated and then in block  1003  checked that it has been received without error by checking that the FCS field is correct. In block  1003  the PHY rate and the length of the packet may be noted by, for example, examining the preamble and header. Once established that the packet has been received correctly, the monitoring STA  860  may send an ACK but need not. If the one way delay is such that the ACK will not arrive at the legacy STA or AP in time to be accepted, then the sending of an ACK is moot. 
         [0055]    Block  1003  may be followed by block  1004  where the monitoring STA  860  awaits the expected retry packet from the legacy STA or AP  850 . Block  1005  may detect the arrival of a retry packet and may signify this by setting the clear channel assessment (CCA) either by detecting the presence of energy, or by detecting the presence of a valid preamble and header. Once established that a packet is being received, block  1005  may be followed by block  1006  where the retry bit and the MAC header fields may be checked to determine if the received packet is the expected retry. If the received packet is not the expected retry, then the process may return to block  1005 . If in block  1006  it is determined that the received packet is the expected retry packet then in block  1007  the trigger time may be extracted. 
         [0056]    There are set times within a received packet that may be used as a trigger. For example, the reception of any particular field could be used as the trigger time. In one embodiment, the time that CCA is exerted, the end of the preamble and header, or the end of the MAC Header field may be used as the trigger time. The time when the end of the MAC Header is received can provide a good indication if the received packet is the expected retry packet, or not, so hence, it represents a good candidate for the timing trigger. The actual trigger signal need not necessarily be the end of the MAC Header. For example, if CCA is used, then this may be the actual trigger signal and then the time to the end of the MAC Header can be calculated. Having extracted the trigger time in block  1007 , calculations of the packet duration and the wait time may be performed in block  1008 . The wait time, Tw, is the time after the trigger time that shall elapse before the monitoring STA  860  transmits the ACK  820  as described with reference to  FIG. 8 . 
         [0057]    Tw=L−26−Ttr+SIFS, where L is the packet duration, δ is the one way delay, Ttr is the trigger time and SIFS is aSIFSTime. 
         [0058]    At time Tw after the trigger time Ttr, the monitoring STA  860  may transmit the ACK, at block  1009 . It is not necessary for the monitoring STA  860  to receive the complete retry packet as it has already been received correctly as checked in block  1003 . Hence, the monitoring STA  860  may stop receiving the packet, switch to transmit mode and send the ACK, or may use a separate transmit path to send the ACK. 
         [0059]      FIG. 11  illustrates method  1100  according to an embodiment of the disclosure as used by the monitoring STA  860  when the delay between the monitoring STA  860  and the target STA or AP  850  exceeds the limit where the standard ACKTimeout interval will timeout before any ACKs will be received. Method  1100  may include block  1110  where the propagation delay for signals sent to or received from the target, which may be an AP or a STA, is estimated. Block  1110  may start with block  1111  where the monitoring STA  860  sends a ranging packet to the target. This ranging packet may be any packet where the turnaround time of the expected response is known. For example, the ranging packet may be an RTS packet, or a data null packet where the CTS or ACK response, respectively, turnaround time should be aSIFSTime. Block  1111  may be followed by block  1112  where the monitoring STA  860  receives the response. Block  1112  may be followed by block  1113  where, as previously described in  FIG. 5  and  FIG. 6 , the propagation delay δ is estimated based upon the received time of the response at the monitoring STA  860  and, in some embodiments, the results stored. Block  1113  may be followed by block  1114  where the decision to repeat the estimation of the delay is made. The decision to repeat the delay estimation may be based upon the movement of the monitoring STA  860 . For example, if the monitoring STA  860  is on a moving platform, then block  1110  may be repeated at a regular period commensurate with the change in range. It may be that repeating block  1110  may result in a location for the target being calculated, and in this case, if the position of the monitoring STA  860  is also known, then the range to the target, and hence the delay, may be calculated and the estimation block  1110  need not be repeated. 
         [0060]    Method  1100  may include block  1120  where the monitoring STA  860  transmits packets to the target. Block  1120  may include block  1121  where the monitoring STA  860  transmits a packet to the target. Block  1120  may be followed by block  1122  where the monitoring STA adjusts the ACKTimeout interval to be used for the expected return ACK such that it accounts for the expected delay δ. For example, the ACKTimeout interval may be increased by a value of 2δ to account for the delay. Hence, in block  1123 , the monitoring STA  860  may wait for the adjusted ACKTimeout interval in order to receive the expected ACK. The calculation of the adjusted ACKTimeout interval may take place every time that the value for the delay δ is updated in block  1113 . If the ACK is received, then in block  1124  the monitoring STA  860  may either send another packet by returning to block  1121 , or end. If, in block  1125 , the expected ACK is not received within the adjusted ACKTimeout interval, then the monitoring STA  860  may assume that the packet failed and hence transmit a retry packet. If subsequent transmitted packets also do not result in an ACK being received within the adjusted ACKTimeout interval, then in block  1126 , the monitoring STA  860  may retry the packet up to a retry limit. This retry limit may be the same or may be higher than the limit that is normally used. 
         [0061]    Method  1100  may include block  1130  where the monitoring STA  860  receives packets from the target. Block  1130  may start with block  1131  where a packet is received. Block  1131  may be followed by block  1132  where the received packet MAC header is checked to determine if the received packet is a new packet or a retried packet. If it is determined in block  1132  that the received packet is a new packet, or indeed a retry packet of a packet that has previously not been received error free, then the complete packet may be received and checked to ensure it is error free. This may be determined by checking the FCS field at the end of the packet. It is not necessary to send an ACK response because, in the case under consideration, the delay δ is too large in that the standard ACKTimeout interval that will be in use at the target will time out before the ACK may be received. If in block  1132  it is determined that this received packet is a retry, and it is the retry of a packet that has previously been received error free, then block  1132  may be followed by block  1134  where the timing trigger is detected as previously described with reference to  FIG. 8 . Block  1134  may be followed by block  1135  where the time to send the ACK response is calculated, again as described with reference to  FIG. 8  and  FIG. 10  block  1008 . Block  1135  may be followed by block  1136  where the ACK is transmitted at the time determined by the calculation in block  1135 . The method may then return to block  1131  to await the next packet. 
         [0062]    The presence or the ability to access an actual trigger signal from a receiver may vary between different implementations. For example, it may be possible to determine the time when CCA is exerted, but not the end of the MAC Header. In such cases, a variation to the above description may be that the CCA trigger signal is used and the ACK transmission time based on that. In this case, it may not be known that the received packet is indeed the expected retry packet, but the consequences are that the packet would be retried again if ACKs collide. At the end of the received packet, the receiver will know if the packet was the expected retry, and if not, the receiver awaits another packet until the retry is received. 
         [0063]    A wireless communication device  1200  which according to an embodiment of the disclosure may be used as the monitoring station is described with reference to  FIG. 12 . 
         [0064]    The wireless communication device, i.e., monitoring station,  1200  may be any device capable of wirelessly receiving signals and transmitting signals and can execute any of the methods illustrated in the specification. Wireless communication device  1200  may be one or more stations or access points, and the like. Wireless communication device  1200  may be one or more wireless devices that are based upon the IEEE 802.11 specification. The wireless communication device  1200  may include a wireless station  1210  and a wireless station  1250 . In one embodiment, the wireless station  1210  may be used as a receiver and wireless station  1250  may be used as a transmitter or vice versa. In another embodiment, wireless station  1210  may be used as a transmitter and a receiver and wireless station  1250  not used, or vice versa. In another embodiment, both wireless stations  1210  and  1250  may be used as transmitters and receivers. It will be appreciated by persons skilled in the art that various combinations of transmitter and receiver may be used. The embodiment to be described herein is that where wireless station  1210  is used as a transmitter/receiver and station  1250  is used as a transmitter. 
         [0065]    The wireless communication device  1200  may also include a time clock  1260  and a processor  1280  which are interconnected to the two wireless communication stations  1210  and  1250  by a data bus  1290 . 
         [0066]    Station  1210  includes interface  1211 , one or more wireless antennas such as wireless antennas  1214  and processing circuitry  1215 . Processing circuitry includes processor  1212  and memory  1213 . In addition to a traditional processor and memory, processing circuitry  1215  may comprise integrated circuitry for processing and/or control, e.g., one or more processors and/or processor cores and/or FPGAs (Field Programmable Gate Array) and/or ASICs (Application Specific Integrated Circuitry). Processing circuitry  1215  may comprise and/or be connected to and/or be configured for accessing (e.g., writing to and/or reading from) memory  1213 , which may comprise any kind of volatile and/or non-volatile memory, e.g., cache and/or buffer memory and/or RAM (Random Access Memory) and/or ROM (Read-Only Memory) and/or optical memory and/or EPROM (Erasable Programmable Read-Only Memory). Such memory  1213  may be configured to store code executable by control circuitry and/or other data, e.g., data pertaining to communication, e.g., configuration and/or address data of nodes, etc. Processing circuitry  1215  may be configured to control any of the methods described herein and/or to cause such methods to be performed. 
         [0067]    The interface  1211  may include an analog and/or digital front end plus the baseband and MAC elements of a receiver. The interface  1211  and/or the processor  1212  may include elements for measuring and/or calculating attributes of received signals (input signals). Memory  1213  stores instructions that, when executed, configure the processor  1212  to monitor communications such as communications between a monitoring station and a wireless device. Interface  1211  is configured to receive a first data packet and a subsequent data packet from the wireless device. Via retransmission determinator  1216 , processor  1212  is configured to determine that receipt of a first data packet from the wireless device has been received without error and determine that a subsequent data packet being received from the wireless device is a retransmission of the first data packet. Interface  1251  is configured to transmit a first acknowledgement to the wireless device before the subsequent data packet is received in its entirety. 
         [0068]    Station  1250  may include interface  1251 , one or more wireless antennas such as wireless antennas  1254 , and processing circuitry  1255 . Processing circuitry  1255  includes processor  1252  and memory  1253 . In addition to a traditional processor and memory, processing circuitry  1255  may comprise integrated circuitry for processing and/or control, e.g., one or more processors and/or processor cores and/or FPGAs (Field Programmable Gate Array) and/or ASICs (Application Specific Integrated Circuitry). Processing circuitry  1255  may comprise and/or be connected to and/or be configured for accessing (e.g., writing to and/or reading from) memory  1253 , which may comprise any kind of volatile and/or non-volatile memory, e.g., cache and/or buffer memory and/or RAM (Random Access Memory) and/or ROM (Read-Only Memory) and/or optical memory and/or EPROM (Erasable Programmable Read-Only Memory). Such memory  1253  may be configured to store code executable by control circuitry and/or other data, e.g., data pertaining to communication, e.g., configuration and/or address data of nodes, etc. Processing circuitry  1255  may be configured to control any of the methods described herein and/or to cause such methods to be performed. 
         [0069]    The interface  1251  may be a wireless transmitter. It may include, for example, at least a part of an analog and/or digital front end of a transmitter. The interface  1251  and/or the processor  1252  may include elements for processing management, data and control packets for transmission via the antenna  1254 . The interface  1251  and/or the processor  1252  may include elements for the transmission of packets via antenna  1254 . 
         [0070]    According to this embodiment of the disclosure, the interface  1211  is arranged to receive input signals and the processor  1212  is arranged to measure and monitor an input signal&#39;s attributes, including but not limited to the preamble and MAC header according to the IEEE 802.11 standard. Also, the interface  1211  is arranged to receive input signals and the processor  1212  is arranged to measure and monitor an input signal&#39;s attributes, including data and control packets transmitted by an access point or station that is based upon the IEEE 802.11. Such control packets include ACK and CTS packets. The memory  1213  may store instructions for executing any method mentioned in the present disclosure, input signals, and results of processing of the processor  1212 , signals to be outputted and the like. 
         [0071]    According to an embodiment of the disclosure, the interface  1251  is arranged to transmit signals and the processor  1252  is arranged to prepare the transmitted signal attributes based upon the IEEE 802.11 standard. Such transmitted packets include control packets based upon the IEEE 802.11 standard. Such control packets include ACK packets. The memory module  1253  may store instructions for executing any method mentioned in the present disclosure, input signals, and results of processing of the processor  1212 , signals to be outputted and the like. 
         [0072]    According to an embodiment of the disclosure, the interface  1211  is arranged to receive transmissions of another wireless communication device and, together with the processor  1212 , is arranged to monitor an attribute of the received transmissions of the other wireless communication device, and determine the attributes of the preamble header and MAC header. In addition, according to an embodiment of the disclosure, the interface  1211  is arranged to measure the time of arrival of the received transmissions of the other wireless device. In addition, according to an embodiment of the disclosure, the interface  1211  is arranged to measure the specific times of the reception of the MAC header of transmissions from the wireless station  1250 . These times may be accomplished by outputting the value of the TSF timer of the wireless communication device  1210  at the point where the MAC header is detected. This may also be accomplished by outputting a trigger that is timed to coincide with the reception of the MAC header from the other wireless device. This trigger may then be used to read the time from the time clock  1260 . Time clock  1260  may have a precision that is higher than the internal TSF timer that is part of the wireless communications device  1210 . Processor  1212  together with memory  1213  may process the information within the MAC header so as to determine the attributes of the received packet. 
         [0073]    According to an embodiment of the disclosure, the interface  1251  may be arranged to transmit packets to another wireless communication device and the processor  1252  may be arranged to prepare the attributes of the packet to be transmitted. 
         [0074]    According to an embodiment of the disclosure, processor  1280  may be used to control the operations of the monitoring station  1200  and in particular the two wireless stations  1210  and  1250 . Processor  1280  may also carry out the various calculations as described in this disclosure and may also prepare the measurement results for disclosure to an operator or user. 
         [0075]    In a further embodiment of this disclosure, the wireless device  1200  may include additional wireless devices that are used as receivers. Some or all of these receivers may then be used to identify the correct retry packet in the case that the reception is such that many packets are being received from other networks and devices. The chance that the wanted packet is received and detected from among a multitude of packets is enhanced by using more receivers. 
         [0076]      FIG. 13  illustrates a method ( 1300 ) for long range communication between a monitoring station, i.e., monitoring station  1210  and a wireless device according to an embodiment of the present disclosure. Initially, processor  1212  of monitoring station  1210  is configured to determine that receipt of a first data packet is received from the wireless device without error (step  1310 ). Interface  1211  is configured to receive a subsequent data packet at the monitoring station from the wireless device (step  1320 ). Processor  1212  or retransmission determinator  1216  is configured to determine that the subsequent data packet being received from the wireless device is a retransmission of the first data packet (step  1330 ). Interface  1211  transmits a first acknowledgment to the wireless device before the subsequent data packet is received in its entirety (step  1340 ). 
         [0077]    In one embodiment, determining that the subsequent data packet being received from the wireless device is a retransmission of the first data packet includes checking a media access control (MAC) header of the received first data packet. In another embodiment, determining that the first data packet was received from the wireless device without error includes checking a field of the data packet. In another embodiment, the field that is checked is the frame check sum (FCS) field. In another embodiment, processor  1212  may be further configured to determine a time of reception of a field of the subsequent data packet, determine a trigger time based on the time of reception of a field of the subsequent data packet, and determine a time interval before transmitting a first acknowledgement, the time interval based upon the trigger time. Interface  1211  may be configured to transmit the first acknowledgement to the wireless device after the time interval has elapsed and before the subsequent data packet is received in its entirety. In another embodiment, processor  1212  of the monitoring station is further is further configured to stop receipt of the subsequent data packet from the wireless device. In another embodiment, interface  1211  is further configured to transmit a ranging packet from the monitoring device to the wireless device, and receive a ranging packet response from the wireless device. Processor  1212  is further configured to estimate a propagation delay based upon a time the ranging packet response was received. In another embodiment, the trigger time is further based upon the propagation delay. In another embodiment, the wireless device is an access point (AP). In another embodiment, the wireless device is a second monitoring station. 
         [0078]    In another embodiment, a method for long range communications between a monitoring station, i.e. monitoring station  1210  and a wireless device is provided. Processor  1212  is configured to determine that receipt of a first data packet from the wireless device has been received without error. Processor  1212  or retransmission determination module  1216  is configured to determine that a subsequent data packet being received from the wireless device is a retransmission of the first data packet by checking a media access control (MAC) header of the received first data packet. Processor  1212  is configured to determine a time of reception of a field of the subsequent data packet to determine a trigger time, and determine a time interval before transmitting a first acknowledgement, the time interval based upon the trigger time. Interface  1211  is configured to transmit the first acknowledgement to the wireless device after the time interval has elapsed and before the subsequent data packet is received in its entirety. 
         [0079]    As will be appreciated by one of skill in the art, the concepts described herein may be embodied as a method, data processing system, and/or computer program product. Accordingly, the concepts described herein may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects all generally referred to herein as a “circuit” or “module.” Furthermore, the disclosure may take the form of a computer program product on a tangible computer usable storage medium having computer program code embodied in the medium that can be executed by a computer. Any suitable tangible computer readable medium may be utilized including hard disks, CD ROMs, optical storage devices, or magnetic storage devices. 
         [0080]    Some embodiments are described herein with reference to flowchart illustrations and/or block diagrams of methods, systems and computer program products. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer (which when programmed as described herein forms a special purpose computer), special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. 
         [0081]    These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer readable memory produce an article of manufacture including instruction means which implement the function/act specified in the flowchart and/or block diagram block or blocks. 
         [0082]    The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. 
         [0083]    It is to be understood that the functions/acts noted in the blocks may occur out of the order noted in the operational illustrations. For example, two blocks shown in succession may in fact be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending upon the functionality/acts involved. Although some of the diagrams include arrows on communication paths to show a primary direction of communication, it is to be understood that communication may occur in the opposite direction to the depicted arrows. 
         [0084]    Computer program code for carrying out operations of the concepts described herein may be written in an object oriented programming language such as Java® or C++. However, the computer program code for carrying out operations of the disclosure may also be written in conventional procedural programming languages, such as the “C” programming language. The program code may execute entirely on the user&#39;s computer, partly on the user&#39;s computer, as a stand-alone software package, partly on the user&#39;s computer and partly on a remote computer or entirely on the remote computer. In the latter scenario, the remote computer may be connected to the user&#39;s computer through a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider). 
         [0085]    While the above description contains many specifics, these should not be construed as limitations on the scope, but rather as an exemplification of several embodiments thereof. Many other variants are possible including, for examples: the use of other specific points within the received packet as the timing trigger, the use of one or more wireless devices to process the delay, the use of one or more wireless devices to transmit the ACK that is sent before the received packet has completed, the calculation and value of the adjusted ACKTimeout interval based upon the measured or estimated delay, the method of estimating the delay. Accordingly the scope should be determined not by the embodiments illustrated, but by the claims and their legal equivalents. 
         [0086]    It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings without departing from the scope.