System and method for reception of wireless local area network packets with bit errors

A method in a first wireless device (WD) supporting wireless communication with a second WD is described. A plurality of wireless packets is received from the second WD including at least a first wireless packet. At least another wireless packet of the plurality of wireless packets is one of a retry packet and a repeat packet of the first packet. Each wireless packet of the plurality of wireless packets includes a plurality of bits and a first group of bits. For each received wireless packet, the plurality of bits corresponding to the received wireless packet is de-spread, and the first group of bits is correlated with a predetermined group of bits. The method further includes performing a majority vote based on the correlation of the first group of bits of each received wireless packet and creating a corrected packet based in part on the majority vote.

TECHNICAL FIELD

The present disclosure relates to wireless communications, and in particular to a monitoring station and method for the reception of packets with bit errors from a target wireless device.

BACKGROUND

The present disclosure relates to communication between devices, where the communication is based upon IEEE 802.11 technology commonly known as Wi-Fi. IEEE Standard 802.11-2016 is used as a reference for some specifications used in the present disclosure. Standard exchange of packets between two stations (STAs), such as between a STA A and STA B, involves the STA A transmitting a packet to STA B and then waiting for an 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 a case where STA A is an AP and STA B is a station, STA. After the AP has transmitted the packet to a STA, the AP will wait for a set timeout period. 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. If, at the STA, the packet is received with errors, then the STA will not transmit an ACK. 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.

FIG.1is a block diagram depicting a monitoring station100receiving a communication packet from a target station110, e.g., a legacy Wi-Fi station such as a known Wi-Fi station. The monitoring station100and the target station110, e.g., the legacy Wi-Fi station, are at a distance d150apart. As the distance d150increases, the received signal level and the signal-to-noise ratio, SNR, at the monitoring station100lowers, and the point may be reached where the received signal level at the monitoring station100is such that the communication packet is received with bit errors and, as discussed above, the packet fails. Any obstruction losses between the target station110, e.g., the legacy Wi-Fi station, and the monitoring station100may also contribute to low SNR.

FIG.2is a diagram showing a format of a direct sequence spread spectrum, DSSS, packet200, e.g., a data or management packet, that complies with the Standard. The direct sequence spread spectrum, DSSS, system is described in Clause 15 of the Standard. Each bit is spread with an 11-bit Barker code spreading sequence. A packet comprises a physical layer, PHY, preamble210, a PHY header220and medium access control, MAC, protocol data unit, MPDU,230. The PHY preamble210comprises two subfields, SYNC211, and start of frame delimiter SFD212. The PHY header220comprises four subfields: Signal221, Service222, Length223, and cyclic redundancy check CRC224. The MPDU230is comprised of the following fields/sub-fields: Frame Control231, Duration232, Address1233, Address2234, Address3235, and Sequence Control236, which together comprise the MAC Header239, plus the Frame Body237, and frame check sum FCS238.

All the bits in the packet200, e.g., DSSS packet, are scrambled with a polynomial G(z)=Z−7+Z−4+1 before being transmitted. Hence, the raw received bits, after de-spreading, are the scrambled bits which are then de-scrambled in order to reproduce the original bit stream. Any raw bits that are received in error, when de-scrambled, result in 3 out of the next 8 de-scrambled bits also being in error. The CRC224is used to protect the contents of the Signal221, Service222and Length223fields/subfields. The FCS238is a 32-bit field containing a 32-bit CRC. The FCS is calculated over all of the other fields of the MPDU230. Therefore, in order for a DSSS packet to be successfully received, there must not be any error in any of the raw received bits. If either the CRC or FCS checks are not correct, then the packet is deemed to have failed and no ACK packet is sent in response. The expected behavior is that the packet will then be retransmitted as a “retry” with the Retry bit241in the Frame Control231set to 1. The Type242and Subtype243fields in the Frame Control231, define the type of packet, e.g., data, or management (e.g., probe request or response, association request or response).

A packet may be re-tried up to a “retry limit” which is set by the station transmitting the packet. As the SNR of the received packet decreases, the possibility of a bit being received in error increases. For example, as the range increases, in the general sense, the SNR will decrease, and there exists a limitation to the range at which a packet may be received without bit errors.

SUMMARY

The present disclosure advantageously provides a method, an apparatus and a measuring station for receiving wireless packets with bit errors and/or creating at least a corrected packet based in part on a majority vote.

In one aspect of the disclosure, a method in a first wireless device (WD) supporting wireless communication with a second WD is described. The method comprising receiving a plurality of wireless packets from the second WD including at least a first wireless packet. At least another wireless packet of the plurality of wireless packets is one of a retry packet and a repeat packet of the first packet. Each wireless packet of the plurality of wireless packets comprises a plurality of bits and a first group of bits of the plurality of bits. For each received wireless packet of the plurality of wireless packets, the plurality of bits corresponding to the received wireless packet is de-spread, and the first group of bits is correlated with a predetermined group of bits. The method further includes performing a majority vote based at least in part on the correlation of the first group of bits of each received wireless packet and creating a corrected packet based in part on the majority vote.

In some embodiments, the method further includes, for each received wireless packet of the plurality of wireless packets, storing the de-spread plurality of bits in a first location; de-scrambling the de-spread plurality of bits; storing the de-spread de-scrambled plurality of bits in a second location; determining whether the correlation of the first group of bits in the first location exceeds a predetermined threshold; and storing the received de-spread plurality of bits in the first location in a third location if the correlation of the first group of bits exceeds the predetermined threshold. The majority vote is performed on the plurality of bits of each received wireless packet stored in the third location.

In some other embodiments, each wireless packet of the plurality of wireless packets is a direct sequence spread spectrum (DSSS) packet. Each wireless packet further includes a second group of bits and comprises a plurality of fields. Each field of the plurality of fields includes at least one bit of the plurality of bits. The plurality of fields includes a physical layer (PHY) preamble field, a PHY header field, and medium access control (MAC) header field, a sequence control field, a frame body field, and a frame check sum (FCS) field. The first group of bits including bits of the de-spread plurality of bits that are part of at least one of the PHY preamble field, the PHY header field, and the MAC header field, the second group of bits including bits of the de-spread plurality of bits that are part of at least one of the sequence control field, the frame body field, and the FCS field.

In an embodiment, the plurality of fields further includes a cyclic redundancy check (CRC) field, a length field that is part of the PHY header field, a signal field, and a service field. The method further includes, for each received wireless packet: performing a CRC check of bits, the CRC check of bits including determining whether a CRC value of PHY header field bits that stored in the first location is correct; if the CRC value is correct, determining a value of the length field; if the CRC value is incorrect and a value of at least one of the signal field and the service field is incorrect: correcting the value of at least one of the signal field and the service field; performing the CRC check of bits; and if the CRC value is correct, determining the value of the length field.

In another embodiment, the plurality of fields further includes a cyclic redundancy check (CRC) field and a length field that is part of the PHY header field. Further, the method includes, for each received wireless packet: determining a number of de-spread bits stored in the first location; determining a value of the length field based upon the determined number of de-spread bits; and determining a CRC value using the determined value of the length field.

In some embodiments, the first group of bits are scrambled bits that are error free. The first group of bits has a first total number of bits, the predetermined group of bits has bits of the de-spread plurality of bits, and the predetermined group of bits has a second total number of bits. The first total number of bits and the second total number of bits being equal.

In some other embodiments, the first total number of bits is determined based in part on one value of at least one field of the plurality of fields and an estimated value of at least another field of the plurality of fields.

In an embodiment, the majority vote is performed if there is an odd number, greater than 1, of received wireless packets. Creating the corrected packet includes: assembling a new plurality of scrambled bits based on the majority vote; de-scrambling the new plurality of scrambled bits; and creating the corrected packet further from the de-scrambled new plurality of scrambled bits.

In another embodiment, the method further includes determining the corrected packet is error free by performing a frame check sum (FCS); and transmitting an acknowledgement (ACK) signal to the second WD.

In some embodiments, the plurality of fields further includes a duration field, a retry field, a type field, and a subtype field. Further, the method includes: setting a value of the duration field to a predetermined duration field value; setting a value of the retry field to 0 for a first received wireless packet and the value of the retry field to 1 for a second received wireless packet; and setting each of a value of the type field to a predetermined type field value and a value of the subtype field to a predetermined subtype field value.

In another aspect, a first wireless device (WD) supporting wireless communication with a second WD is described. The first WD comprises a transmitter receiver configured to receive a plurality of wireless packets from the second WD including at least a first wireless packet. At least another wireless packet of the plurality of wireless packets is one of a retry packet and a repeat packet of the first packet. Each wireless packet of the plurality of wireless packets comprises a plurality of bits and a first group of bits of the plurality of bits. The first WD further comprise processing circuitry in communication with the transmitter receiver. The processing circuitry is configured to, for each received wireless packet of the plurality of wireless packets de-spread the plurality of bits corresponding to the received wireless packet and correlate the first group of bits with a predetermined group of bits. Further, the processing circuitry is configured to perform a majority vote based at least in part on the correlation of the first group of bits of each received wireless packet and create a corrected packet based in part on the majority vote.

In some embodiments, the processing circuitry is further configured to, for each received wireless packet of the plurality of wireless packets: store the de-spread plurality of bits in a first location; de-scramble the de-spread plurality of bits; store the de-spread de-scrambled plurality of bits in a second location; determine whether the correlation of the first group of bits in the first location exceeds a predetermined threshold; and store the received de-spread plurality of bits in the first location in a third location if the correlation of the first group of bits exceeds the predetermined threshold. The majority vote being performed on the plurality of bits of each received wireless packet stored in the third location.

In some other embodiments, each wireless packet of the plurality of wireless packets is a direct sequence spread spectrum (DSSS) packet. Each wireless packet further includes a second group of bits comprising a plurality of fields. Each field of the plurality of fields includes at least one bit of the plurality of bits. The plurality of fields includes a physical layer (PHY) preamble field, a PHY header field, and medium access control (MAC) header field, a sequence control field, a frame body field, and a frame check sum (FCS) field. The first group of bits includes bits of the de-spread plurality of bits that are part of at least one of the PHY preamble field, the PHY header field, and the MAC header field. The second group of bits including bits of the de-spread plurality of bits that are part of at least one of the sequence control field, the frame body field, and the FCS field.

In an embodiment, the plurality of fields further includes a cyclic redundancy check (CRC) field, a length field that is part of the PHY header field, a signal field, and a service field. The processing circuitry is further configured to, for each received wireless packet: perform a CRC check of bits, the CRC check of bits including determining whether a CRC value of PHY header field bits that stored in the first location is correct; if the CRC value is correct, determine a value of the length field; if the CRC value is incorrect and a value of at least one of the signal field and the service field is incorrect: correct the value of at least one of the signal field and the service field; perform the CRC check of bits; and if the CRC value is correct, determine the value of the length field.

In another embodiment, the plurality of fields further includes a cyclic redundancy check (CRC) field and a length field that is part of the PHY header field. The processing circuitry is further configured to, for each received wireless packet: determine a number of de-spread bits stored in the first location; determine a value of the length field based upon the determined number of de-spread bits; and determine a CRC value using the determined value of the length field.

In some embodiments, the first group of bits are scrambled bits that are error free. The first group of bits has a first total number of bits. The predetermined group of bits includes bits of the de-spread plurality of bits and has a second total number of bits. The first total number of bits and the second total number of bits are equal. The first total number of bits are determined based in part on one value of at least one field of the plurality of fields and an estimated value of at least another field of the plurality of fields.

In some other embodiments, the majority vote is performed if there is an odd number, greater than 1, of received wireless packets. Creating the corrected packet includes: assembling a new plurality of scrambled bits based on the majority vote; de-scrambling the new plurality of scrambled bits; and creating the corrected packet further from the de-scrambled new plurality of scrambled bits.

In an embodiment, the processing circuitry is further configured to determine the corrected packet is error free by performing a frame check sum (FCS) and transmit an acknowledgement (ACK) signal to the second WD.

In another embodiment, the plurality of fields further includes a duration field, a retry field, a type field, and a subtype field. The processing circuitry is further configured to: set a value of the duration field to a predetermined duration field value; set a value of the retry field to 0 for a first received wireless packet and the value of the retry field to 1 for a second received wireless packet; set each of a value of the type field to a predetermined type field value and a value of the subtype field to a predetermined subtype field value.

In yet another aspect, a measuring station comprising a first wireless device (WD) supporting wireless communication with a second WD is described. The first WD includes a transmitter receiver configured to receive a plurality of wireless packets from the second WD including at least a first wireless packet. At least another wireless packet of the plurality of wireless packets is one of a retry packet and a repeat packet of the first packet. Each wireless packet of the plurality of wireless packets includes a plurality of bits and a first group of bits of the plurality of bits. The first WD further includes processing circuitry in communication with the transmitter receiver. The processing circuitry is configured to, for each received wireless packet of the plurality of wireless packets: de-spread the plurality of bits corresponding to the received wireless packet; correlate the first group of bits with a predetermined group of bits; and determine whether the correlation of the first group of bits exceeds a predetermined threshold. The processing circuitry is further configured to perform a majority vote on the plurality of bits of each received wireless packet for which the correlation of the first group of bits exceeds the predetermined threshold and create a corrected packet based in part on the majority vote.

DETAILED DESCRIPTION

This disclosure provides methods and devices for the correction of data or management packets received with bit errors for devices that are based upon the IEEE 802.11 technology, commonly known as Wi-Fi. In some embodiments, this disclosure provides solutions for cases where a monitoring station100receives a series of a packet plus retries, each with bit errors, from a target station110, e.g., a legacy Wi-Fi station. The target station110, e.g., the legacy Wi-Fi station is one that complies with the 802.11 Standard, generally known as Wi-Fi. The monitoring station100is one that generally complies with the 802.11 Standard but has been modified, as described in this disclosure, to receive and correct a series of a packet plus retries, each with bit errors, from a target station110, e.g., a legacy Wi-Fi station. Although the embodiments disclosed herein relate to Wi-Fi communications, the disclosure is not limited to Wi-Fi communications, and may be applied to other types of communications between wireless devices.

Methods to overcome and correct the reception of a series of a received packet plus retries, each with bit errors, are described herein. Also, methods are disclosed that enable the monitoring station100to receive packets from a target station110, e.g., a legacy Wi-Fi station, at extended ranges or at lower SNRs than would be the norm. The packets from the target station110, e.g., the legacy Wi-Fi station, may be referred to as “wanted” packets”. The target station110, e.g., t legacy Wi-Fi station, may be a device such as a station (STA) or an access point (AP). In the above and following description, the legacy Wi-Fi station is referred to as the “target station110”, and is generally described as an AP as this aids in the descriptive process. However, the disclosure is not limited solely to such an arrangement.

This disclosure uses the processes of “auto-correlation” and “majority voting”. When receiving re-tried packets with errors, auto correlation may be used on the part of the packet(s) that is known a priori, such that it may be confirmed that the received packet is indeed the wanted packet, whereas majority voting may be used on the individual bits of the repeated, re-tried, parts of the packet in order to attempt to recover the correct bits. 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 outline description of the application of auto-correlation and majority voting on re-tried DSSS packets.

Auto-correlation works by passing a known pattern across a noisy pattern. For example, the known pattern may comprise the initial bits of the received packet. With reference toFIG.2, if the target station110is known, then, when receiving a wanted packet from that device, all the bits of the PHY preamble210and PHY header220are known a priori, with the possible exception of the Length field223. Similarly, the bits of the Frame Control field231, and in particular, the three address fields233,234and235are known a priori. In addition, the value of the Duration field232may be assumed to be a standard value (e.g., 314) that covers the short interframe space SIFS and the time to transmit an ACK. If the value of the Length field223is known, then all the 368 received bits, up to the Sequence Control236are known and hence the raw scrambled bits, up to the Sequence Control field236, can be determined. As described above, all bits are scrambled with a polynomial G(z)=Z−7+Z−4+1 before being transmitted. In determining the scrambled bits, it is necessary that all the bits are known. If a bit is in error, then the rest of the scrambled bit stream likely will have a multitude of errors. Hence, in order to determine an accurate, scrambled 368-bit stream up to the Sequence Control236, the values of the Length223and CRC224fields must be correct. The Length field223is the duration of the MPDU230, in microseconds, hence by measuring the time or number of bits that are detected by Barker code correlations, the number of bits in the packet200may be determined. If the number of bits in the packet200are known, then the values of the Length field223and the CRC field224can be calculated and then, by assuming a value for the Duration field232, the raw bit stream, i.e., scrambled bit stream, may be derived for the PHY preamble210, PHY header220, and the MAC Header239, with the possible exception of the Sequence Control236. A correlation of the first 368 bits can provide a very high probability that the received packet is the wanted packet. It is understood that the fields/subfields of any packet and/or signal described herein may be referred to by the field/subfield name alone or by the field/subfield name and the term “field” or the term “subfield,” e.g., Length223or Length field223.

Correlation cannot be used on the Frame body237as the data therein is unknown. If the packet200is retried several times, however, a majority vote may be taken on each scrambled bit and then the Frame Body237may be re-created. Similarly, majority voting on the FCS field238bits may enable the FCS to be recreated. After majority voting has been carried out on the individual scrambled bits of the Frame Body237and FCS238, the complete scrambled packet may be assembled and then de-scrambled. The resulting FCS may then be used to check that the complete packet has been re-assembled correctly.

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 descriptions of majority voting and auto-correlation and derivations of their relative performances when applied to re-tried packets, as discussed above.

For DSSS 1 Mbps, the probability of a bit error, Pb, for BPSK, is

P⁢b=0.5erfc⁢Eb/N0(1)Where “erfc” is the Gauss complimentary error functionEbis energy per bitN0is noise per hertz

For BPSK, Eb/N0is equal to the signal to noise ratio, SNR

The performance of majority voting is discussed below.

The Binomial Distribution probability mass function provides the probability, Pk, of exactly k successes in n trials.

The cumulative distribution function, CDF, provides the probability that at most k successes in n trials.

For a successful “M out of N” majority vote, in N trials, no more than (N−M) bits can be in error.

For example, with a 3 out of 5 majority vote, in 5 trials, no more than 2 bits may be in error.

Hence, for N trials, with bit error Pb, the probability that at most (N−M) bits are in error, is the

The probability that the vote is incorrect, i.e., the new or effective bit error rate, Pbeff, is:
Pbeff=1−Pk(X≤(N−M))   (2)

For a packet consisting of B bits, with a bit error rate of Pbeff, the packet error rate, PER, is
PER=1−(1−Pbeff)B(3)

The received signal strength, Pr, is given by the standard formula:
Pr=−174+10 log BW+NF+SNR   (4)
Where Bandwidth, BW, is 20 MHz, and let the Noise Figure, NF=3 dB. The bit error rate, Pb for varying SNR is derived from equation (1).

With DSSS, there is a theoretical ˜10 dB processing gain due to the 11 bit Barker code, i.e., Processing Gain=10 Log(11). To account for implementation loss, 9 dB may be assumed for the Barker code processing gain. Hence equation (4) can be modified to:
Pr=−107+SNR   (5)

FIG.3is a graphical representation300of the PER for majority voting of 2 out of 3 (plot302), 3 out of 5 (plot303), 4 out of 7 (plot304), 5 out of 9 (plot305), and 6 out of 11 (plot306) for 1000 bits. The results of PER, as per equation (3), are plotted against the received signal strength Pr, as per equation (5), for B=1000. Plot301is the PER for no majority vote, i.e., a single, 1000 bit packet. For a PER of 0.5, the sensitivity, Pr, for a 6 out of 11 majority vote (plot306), is an improvement of about 9 dB over that for a single 1000 bit packet (plot301).

It is noted thatFIG.3does not account for the extra packets required for the different votes. For example, “6 out of 11” majority vote, plot305, requires 11 packets, whereas the “no voting” plot301result is for just one packet.FIG.4is a graphical representation400of the PER for majority voting of 2 out of 3 (plot402), 3 out of 5 (plot403), 4 out of 7 (plot404), 5 out of 9 (plot405), and 6 out of 11 (plot306) for 1000 bits, for 11 retried packets. Graphical representation400shows that for a PER of 0.5, the sensitivity, Pr, for a 6 out of 11 majority vote (plot306) is an improvement of about 7 dB over that of 11 retried 1000 bit packets (plot401).

As indicated by equation (3), the fewer the number of bits in a packet, the more effective majority voting is.FIG.5is a graphical representation500of PER for 4 out of 7 majority voting, compared to simple retries, for varying number of bits. Plots501,502,503,504,505,506, and507are for 7 retries of single packets of 3000, 2000, 1000, 500, 300, 200 and 100 bits respectively. Plots510,511,512,513,514,515, and516, are for 4 out of 7 majority voting on 7 packets of 3000, 2000, 1000, 500, 300, 200 and 100 bits respectively. Graphical representation500shows that the less bits the more effective is majority voting.

Correlation works by passing the known pattern across the noisy pattern, and if the bits/symbols agree, “correlate” or match, they add, if not, they subtract.

For a packet of B bits, B.Pb bits will not match and B(1−Pb) will match,

Note that for pure noise, Pb=0.5 and the correlation will be 0%.

For a given SNR, the bit error Pb may be calculated using equation (1) and the correlation calculated using equation (6). The variance and standard deviation, σ, of the mismatched bits may be calculated:
σ2=B Pb(1−Pb)
σ=√{square root over (B Pb(1−Pb))}  (7)

For B bits, the number of mismatched bits is B Pb, with a standard deviation of σ. Hence, the number of mismatched bits=B.Pb±σ, and the number of matched bits is B−(B.Pb±σ).

Thus, the correlation is given by:

Comparing (8) to (6), the following associations can be made:
Correlation mean=(1−2Pb)   (9)
and Correlation standard deviation=2σ/B.   (10)

Noise has a bit error rate, Pb=0.5 with a mean of zero and thus, from equation (7),

σ=B/4,
and from equation (10)

Note that the correlation mean is independent of the number of bits that are correlated. It is the standard deviation that changes; the more bits, the smaller the deviation. Note that (11) represents a thermal noise case and any increased background noise must be accounted for. For example, in the case of 3 dB and 6 dB noise figure, as used in (4) and (5), equation (11) would be modified to

noise correlation standard deviation,

noise correlation standard deviation,

For example, from (13) for a Correlation of 50%, 75% of the bits will be correct.

As discussed above, if the length of a packet is unknown, a measurement of the length of the packet is fundamental to being able to determine if the received packet is the one that is of interest, i.e., so that the address fields233,234, and235can be checked to be correct. A correlation of the first 368 bits can provide a very high probability that the received packet is the wanted packet.

Three example methods of determining the value of the Length field223are discussed. First, if the CRC field224value is received correctly, then the Length field223value is known even if the FCS does not check correctly. Second, the values of the Signal field221and the Service field222are known a priori, hence, if the CRC field224value is not correct, and there are errors in either or both of the Signal221and Service222fields, the correct values for the fields can be inserted and then the CRC field224value re-checked. If the CRC is correct, then the values of the Length field223is known. Third, if the first two methods fail, then by monitoring and counting the number of Barker Code correlations, i.e., the number of de-spread bits, the Length field may be determined. The Length field is the duration of the MPDU230, in microseconds. The measurement of the length is somewhat simplified by the fact that the MPDU will always be in octets. For example, if 5 or more out of 8 codes are correct, then it may be assumed that that octet is part of the length.

The 802.11 DSSS waveform uses an 11-chip Barker spreading sequence. When the DSSS receiver operates asynchronously to the transmitter, the receiver must align its own de-spreading process with the 11-chip symbols in the received sample stream. The incoming noisy bit stream may be sampled at 20 Msps and then correlated with the Barker sequence. Every 20 samples a finite impulse response, FIR, filter may output a correlation spike corresponding to the correlation (positive for a 1 and negative for a 0). A threshold may be set for the height of the spike so as to identify the presence of Barker code, i.e., a bit. The number of bits in a packet will also align with octets such that the packet consists of a number of octets. Thus, the correlation over 8 μs (which is 88 Barker code bits) may be used to detect if the packet is still present.

To detect that a Barker code is present, a correlation threshold can be used. The probability that noise can exceed the threshold may be calculated, as follows:

The probability P(X>Y)=P(X−Y>0)=1−P(X−Y≤0)

By independence, (X−Y) is normally distributed with

μ=μ1−μ2 and σ=√{square root over (σ12+σ22)}

Hence

Where ϕ is the distribution function of the N(0,1) distribution.

P⁡(X>Y)=1-P⁡(X-Y≤0)=1-ϕ⁡(-μσ)(15)
For various bit error rates, Pb, the mean correlation for the Barker code is given by equation (9), and the standard deviation by equation (10). For noise the correlation mean is zero and the standard deviation, is given by equation (11), (11A) or (11B).

FIG.6is a graphical representation600of the probability that the Barker code is detected above noise against received signal level Pr, for a NF=6 dB. To account for the bit error rate, Pb, the value for Pr, derived from equations (4) and (5), is modified such that the processing gain due to the Barker code is 10Log [11(1−Pb)]. Plot601is for a single Barker sequence of 11 bits. Plot602is for 4 Barker code sequences, 44 bits, plot603is for 6 code sequences, 66 bits, and plot604is for 8 code sequences, 88 bits. With only 11 bits, plot601, there is always a 5% chance605that noise can resemble the code, even at high signal levels, but as the number of bits increases, the probability that the Barker code is correctly detected increases. At −110 dBm there is about a 95% probability610that 4 Barker sequences exceed noise.

FIG.7is a graphical representation700of the mean correlation701together with the standard deviation702of the correlation, and the noise standard deviation710, of 44 bits (4 Barker sequences) against the received signal strength, Pr, for a NF=6 dB. The probability that the wanted 44 bits exceeds the noise (plot602) is also shown. At Pr=−110 dBm, the mean correlation701is 0.52 720 and the probability that the wanted exceeds the noise is 95%. Hence, the length of the received packet may be reliably measured down to a signal level in the order of −110 dBm.

As discussed above, if the value of the Length field is known, then the first 368 bits of the scrambled packet can be determined, and auto correlation may be performed against the first 368 bits of the received packet in order to determine that the packet is indeed a wanted packet from the target station110, e.g., the legacy Wi-Fi station.

FIG.8is a graphical representation800of an example of mean correlation801together with the standard deviation802of the correlation, the noise standard deviation810, and the noise 3 times standard deviation812, of 368 bits, against the received signal strength, Pr, for a NF=6 dB. At Pr=−110 dBm, the mean correlation801has a value815of about 0.53, and the standard deviation802has a value816of about 0.58. These correlation thresholds are well in excess of the noise 3 times standard deviation812of about 0.31. Hence, correlating the “known” 368 initial bits of the received packets with a threshold of about 0.58 should enable a reliable positive identification of the wanted packet.

At a receive strength of −110 dBm and higher, and with a NF=6dB or less, as discussed above with reference to the examples ofFIGS.6and7, the length of the packet can be reliably measured and the values of the Length field223and the CRC224can be determined. With knowledge of the Addresses fields233,234, and235, the packet bits up to the Sequence Control field236may then be constructed and then scrambled. This scrambled bit stream may then be auto-correlated against the received (scrambled) bit stream and if the correlation exceeds a threshold, e.g., about 0.58, it may be reliably assumed that the received packet is indeed a “wanted” packet from the target station110, e.g., a legacy Wi-Fi station.

Having determined that the received packet is a wanted packet, and knowing the length of the packet, the raw received bits for the Sequence Control field236, Frame Body field237and FCS field238may then be stored. Subsequent retries of the packet can be determined by setting the Retry bit241to one, correlating the initial 368 bits to determine that the received packet is indeed the wanted retried packet, then storing the raw received bits for the Sequence

Control field236, Frame Body field237and FCS field238. As more retried packets are received, then, as discussed above with reference toFIGS.4and5, majority voting may take place on each of the raw bits that have been stored. With reference toFIG.5, the performance of the majority voting, assuming a 4 out of 7, is such that the required received signal level is generally higher than −110 dBm, hence the majority voting performance may be considered to be the limiting factor.

FIG.9illustrates a block diagram of an example wireless communication device900which, according to an embodiment of the disclosure, may be used as or as part of the monitoring station100, i.e., a new version of the monitoring station100.

The wireless communication device900may be a device capable of wirelessly receiving signals and transmitting signals and may be configured to execute any of the methods of the Standard. Wireless communication device900may be one or more stations or access points, and the like. Wireless communication device900may be one or more wireless devices that are based upon the Standard, and each may be configured to act as a transmitter or a receiver. The embodiment described herein is that where wireless communication device900includes a wireless transmitter receiver910and a wireless receiver950. The wireless communication device900may also include a computer system980which is interconnected to the wireless transmitter receiver910and the wireless receiver950by a data bus970.

In some embodiments, the wireless transmitter910includes an RF transmitter911, an RF receiver912, and processing circuitry920that includes processor921, and memory module922. The wireless transmitter receiver910also includes one or more wireless antennas such as wireless antenna914. The RF transmitter911may perform the functions of spreading, and DSSS modulation, as described in the Standard, and amplification for the transmission of the DSSS packets via the wireless antenna914. The RF receiver912may perform low noise amplification for the reception of the DSSS packets via the wireless antenna914and the functions of de-spreading, and DSSS demodulation, as described in the Standard. In some embodiments, the processing circuitry920and/or the processor921may 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) configured to execute programmatic software instructions. In some embodiments, some functions of the RF transmitter911and/or the RF receiver912may be performed by the processing circuitry920. The processing circuitry920may be configured to control any of the methods and/or processes described herein and/or to cause such methods, and/or processes to be performed, e.g., by the RF transmitter911or RF receiver912. The memory module922may be configured to store data, programmatic software code and/or other information described herein. In some embodiments, the software may include instructions that, when executed by the processing circuitry920, causes the processing circuitry920to perform the processes described herein with respect to the wireless transmitter receiver910.

In some embodiments, the wireless receiver950includes an RF front end951, a DSSS receiver952, a correlator953, processing circuitry954(that includes a processor955and a memory module956) and one or more wireless antennas such as wireless antenna957. In some embodiments, the wireless transmitter receiver910and the wireless receiver950may share the same antenna(s). The RF front end951may perform the usual functions of an RF receiver front end such as low noise amplification, filtering, and frequency down conversion so as to condition the received signal suitable for inputting to the DSSS receiver952. The DSSS receiver952may perform the functions of Barker code detection and de-spreading of the DSSS packet so as to condition the received signal suitable for inputting to the correlator953. The correlator953may perform the function of correlating the de-spread received bits with a known expected bit pattern as discussed above with reference toFIGS.6,7and8. In some embodiments, the DSSS receiver952and/or the correlator953and/or the processing circuitry954may 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) configured to execute programmatic software instructions. In some embodiments, the functions of the DSSS receiver952and/or the correlator953may be performed by the processing circuitry954. The processing circuitry954may be configured to control any of the methods and/or processes described herein and/or to cause such methods, and/or processes to be performed, e.g., by the wireless receiver950. The memory module956is configured to store data, programmatic software code and/or other information described herein. In some embodiments, the software may include instructions that, when executed by the processing circuitry954, causes the processing circuitry954to perform the processes described herein with respect to the wireless receiver950.

According to this embodiment of the disclosure, the wireless receiver950and the RF receiver912may be configured to measure and monitor an input signal's attribute, such as may include one or more of data, management and control packets, transmitted by an access point or station that may be based upon the Standard. The memory modules922and956may store instructions for executing any method mentioned in the Standard, input signals, and results of processing of the processors921and955, signals to be outputted and the like.

According to an embodiment of the disclosure, the RF transmitter911may be configured to transmit signals and the processing circuitry920may be configured to prepare the transmitted signal attributes based upon the Standard. Such transmitted packets may include data packets, control packets and management packets that are to be transmitted by a wireless station that is based upon the Standard. The memory module922may store instructions for executing any method mentioned in the specification, input signals, and results of processing of the processor921, signals to be outputted and the like.

According to another embodiment of the disclosure, the RF wireless receiver912may be configured to receive the transmissions of another target station110such as a legacy Wi-Fi station and the processing circuitry920may be configured to monitor attributes of the transmissions of the other wireless communication device.

According to yet another embodiment of the disclosure, the wireless receiver950may be configured to receive the transmissions of another target station such as a target station110, e.g., a legacy Wi-Fi station, and the processing circuitry954may be configured to monitor attributes of the transmissions of the other target station. The DSSS receiver952may be configured to auto-correlate the received transmission with the DSSS Barker code, and de-spread the received signal so as to produce the raw scrambled bit stream as described above with reference toFIGS.6and7. In addition, according to an embodiment of the disclosure, the correlator953may be configured to auto-correlate the first 368 bits of the wanted packet with the received raw scrambled bit stream as discussed above with reference toFIG.8.

According to an embodiment of the disclosure, a computer system980may be used to control the operations of the wireless communication device900and in particular the wireless transmitter receiver910, and wireless receiver950. The computer system980may include an interface981. Interface981may contain a connection to the wireless transmitter receiver910and the wireless receiver950, plus a connection to a display986, a connection to a keyboard and mouse987as well as interfacing to the processing circuitry982. In some embodiments, the processing circuitry982may include a processor983, a memory984, and a database985. The database985may contain the details of target stations, e.g., MAC addresses and the like, and the processor983and memory984may be used to carry out the determinations of the expected scrambled bit streams, the calculations of the majority voting processes, and the de-scrambling and re-construction of the retried received packets. Information on the target station110may be inputted using the keyboard/mouse987. The display986may be used to show the details of the target station and the re-constructed packet information.

Note that the modules discussed herein may be implemented in hardware or a combination of hardware and software. For example, the modules may be implemented by a processor executing software instructions or by application specific integrated circuitry configured to implement the functions attributable to the modules. Also note that the term “connected to” as used herein refers to “being in communication with” and is not intended to mean a physical connection nor a direct connection. It is contemplated that the signal path between one element and another may traverse multiple physical devices.

Thus, in some embodiments, the processing circuitry982may include the memory984and a processor983, the memory984containing instructions which, when executed by the processor983, configure the processor983to perform the one or more functions described herein. In addition to a traditional processor and memory, the processing circuitry982may 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).

The processing circuitry982may include and/or be connected to and/or be configured for accessing (e.g., writing to and/or reading from) the memory984, which may include 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 memory984may 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. The processing circuitry982may be configured to control any of the methods described herein and/or to cause such methods to be performed, e.g., by the processor983. Corresponding instructions may be stored in the memory984, which may be readable and/or readably connected to the processing circuitry982. In other words, the processing circuitry982may include a controller, which may comprise a microprocessor and/or microcontroller and/or FPGA (Field-Programmable Gate Array) device and/or ASIC (Application Specific Integrated Circuit) device. It may be considered that the processing circuitry982includes or may be connected or connectable to memory, which may be configured to be accessible for reading and/or writing by the controller and/or processing circuitry982. It is also noted that the elements of the wireless communication device900can be included in a single physical device/housing or can be distributed among several different physical devices/housings.

FIGS.10and11form a flow diagram of an example of one embodiment of a method1000for the correction of data or management packets, received from a target station110, with bit errors, utilizing the wireless communications device900, which according to an embodiment of the disclosure may be used as or as part of the monitoring station100. The method may start with step1001where the MAC address of the target station110may be entered together with the Type242and Subtype243values of the wanted packet. These values may be entered using the keyboard/mouse987and inputted to the processing circuitry954in the wireless receiver950. The Barker code is detected at step1002to indicate the start of reception of a DSSS packet. If a Barker code is detected at step1002, the bits may be de-spread at step1004. Then at step1006a correlation may be carried out against the PHY preamble210to confirm that a DSSS packet is indeed being received. The Barker code detection may be carried out by the DSSS receiver952. The auto-correlation of the PHY preamble210may be performed by the correlator953with the raw scrambled PHY header bit stream being inputted from the processing circuitry954. If, at step1006the correlation of the PHY header exceeds a threshold, then it may be assumed that a DSSS packet is being received. The decoded, scrambled bit stream may then be saved at step1010and the de-scrambled bit stream may be saved at step1008. The de-scrambling of the received bit stream may be performed by the processing circuitry954and the de-scrambled and scrambled bit streams may be saved in the memory module956via processor955.

At step1012the CRC224may be checked for the de-scrambled bit stream of the PHY header220and if it is correct, then at step1020the value of the Length field223may be saved. If the CRC is not correct, then it is known that there are errors in the PHY header220. The values of the Signal221and Service222fields are known a priori and a check may be made, at step1013, to see if they have been correctly received and, if not, corrected. The CRC check may then be repeated and, if correct, the value for the Length field223is known and may be saved at step1020. If the values for the Signal221and Service222fields were correct in step1013, then it may be assumed that the Length field223is in error. If the CRC was correct at step1012, then at step1022a check on the FCS238may be made. If the FCS value is correct, then at step1024it may be declared that the packet has been received and the method ends. The Signal, Service and CRC checks and the possible replacement of the Service and Signal fields may be performed by the processing circuitry954. The packet may also be received by RF receiver912in wireless transmitter receiver910, and, after de-coding and de-scrambling by the processing circuitry920the FCS is correct, then the packet has been correctly received and wireless receiver950may be informed via the data bus970.

If steps1012and1013both fail then, at step1014, the number of de-coded bits, as stored at step1010, may be counted and the length of the packet may then be calculated, as discussed above with reference toFIGS.6and7. Values for the Length field223and CRC224may then be calculated using the known values of the other fields in the PHY header220. Then, at step1016, a value of 314 may be assumed for the Duration field232and the Retry bit241may be set to zero or one, dependent upon the assumption that this packet is the initial packet or a retry. Also, at step1016the values for the type242and subtype243of the wanted packet may be entered. If, at step1022, the FCS check fails, then the method may advance to step1016. The complete initial 368 scrambled bits of the wanted packet may now be assembled at step1018and at step1026an auto-correlation of the 368 scrambled bits, as determined at step1018, is carried out with the initial 368 raw scrambled bits stored at step1010. If the auto-correlation fails, i.e., as discussed above with reference toFIG.8and the correlation does not exceed a set threshold, then the packet may, at step1030, be discarded and the method returns to step1002. If the auto-correlation is successful, then the method advances toFIG.11, step1101. Steps1013,1014,1016, and1018may all be performed by the processing circuitry954.

At step1101, the entire scrambled packet, as stored at step1010but with the initial 368 bits set as determined at step1018, may be stored. The packet(s) may be stored in memory module956or database985. At step1102a check is made of the number of (retried) packets in the store and if it is an odd number greater than 1, i.e., 3, 5, 7, 9, etc., then a majority vote may be performed, at step1104, on each corresponding scrambled bit of the stored packets, from the Sequence Control field236to the end of the FCS238. If the check at step1102fails, then the method returns to step1002to await a new packet. The process of majority voting is discussed above with reference toFIGS.3,4and5, and equations (2) and (3). Based upon the results of the majority voting in step1104, plus the “known” scrambled bits for the 368 bits of the packet up to the Sequence Control field236, a complete raw scrambled bit stream for the entire packet may be assembled (step1106). In step1108the bit stream may be de-scrambled and at step1110the FCS check may be carried out. If, at step1112, the FCS check is successful, then at step1114the packet may be declared as being received and the method ends. If the FCS check at step1112is not successful, then a check is made at step1116to assess if the maximum number of expected retries has been reached, i.e., can at least two more retried packets be expected? If yes, then the method returns to step1002, but if no, then, at step1118the packet is declared as having failed and the method ends. The processes of majority voting, assembling the scrambled packet, de-scrambling the bit stream, calculating the FCS, and checking the FCS may be all performed by the processing circuitry954and/or the processing circuitry982.

If a value for the maximum number of retries, as used at step1116, is higher than the maximum number of retries that the target station110, e.g., the legacy Wi-Fi station, may be using, or, if too many re-tried packets fail, then a timeout may be required to prevent the method1000from endlessly looping. For example, a timer may be set to start at step1101after the first successful auto-correlation at step1028and if that packet, with re-tries, is not successful, i.e., is not declared “received” at steps1112or1024within a preset time, then that packet may be abandoned. A timeout check at step1116may be used. At step1016the values for the type242and subtype243of the packet may be set. In the event that the type and subtype of the packet are not specifically known then different values may be chosen, in turn, and steps1018,1026and1028repeated until in step1028the threshold is exceeded, or a maximum correlation is found, and thus the values of the type242and subtype243established.

FIG.12is a flowchart of an exemplary process1200that corrects data or management packets, received with bit errors, from a target station110, utilizing the wireless communications device900, which according to an embodiment of the disclosure may be used as or as part of the monitoring station100. The process includes inputting, such as via the keyboard/mouse987, the MAC address and expected type242and subtype243values of the wanted packet from the target station110(step1201). Received symbols, via RF front end951, are correlated with the Barker code, de-coded via the DSSS receiver952, and correlated, via the correlator953, against the PHY preamble210to confirm that a DSSS packet is being received (step1202). The raw received scrambled bit stream is then stored, in “store A”, via the processor955, in the memory module956, of the processing circuitry954(step1206). The scrambled bit stream is also de-scrambled and stored in “store B”, via the processor955, in the memory module956, of the processing circuitry954(step1204). In step1210, the value of the CRC224of the de-scrambled bit stream is checked and if correct the value of the Length field223is noted. If the CRC check fails, then the values of the signal221and service222fields are examined. These values are known a priori and hence if they are not correct, they can be corrected, the CRC checked again and, if correct, the value of the Length field223is noted. If the CRC is still incorrect then the value for the Length field223is estimated by counting the stored raw scrambled bits in “store A”, step1206. Using the estimated length value, a CRC value is calculated. The processes carried out in step1210may be performed by the processing circuitry954.

The process further includes setting the Duration field232, the retry bit,241, the type242and subtype243values and then determining the initial 368 bits of the raw scrambled bit stream of the wanted packet (step1220). In step1222, the initial 368 bits determined in step1220, are auto-correlated against the initial 368 bits of the received raw bit stream stored in step1206, (store A). If the correlation exceeds a preset threshold, then the complete packet, stored at step1206, is added to another store, “store C”. If this is the first packet, then a timeout timer is started. If the correlation does not exceed a preset threshold, then the complete packet, stored at step1206, is assumed to not be a wanted packet, and is discarded. The process further includes step1224where the number packets in store C is checked, and if that number is an odd number greater than 1, then a majority vote is performed on each corresponding bit of the raw bit streams of the packets (store C). The scrambled bit stream is then assembled, based upon the results of the majority voting, and the bit stream then de-scrambled. The FCS check is then carried out in step1226. If the FCS check is successful, then the packet is “received”. If the FCS fails, then it is first checked if the timeout timer is still valid. If not, the packet fails and the process ends. Else, if the FCS fails, it is checked if more retried packets are expected and if so, the process returns to step1202where a new wanted packet is received. In some embodiments, Stores A and B are contained within the memory module956and store C resides in the database985. The process of majority voting takes place via the processing circuitry982and the re-assembly of the packet, de-scrambling and FCS check is also performed in the processing circuitry982.

The received bit stream is also received via the wireless transmitter receiver910(e.g., a standard transmitter receiver), via RF receiver912, de-coded and de-scrambled and processed in the processing circuitry920. If the received packet FCS is correct, and the address fields233,234and235are as expected, then exemplary process1200is not required as the wanted packet has been successfully received.

At step1210if the value of the Length field223is estimated, then the estimated value will be in units of 8 as the MPDU is always a number of octets. If, for example, there are two possible estimates, then each value is used, the corresponding CRC calculated, and steps1220,1222repeated for each value. The higher correlation in step1222is used to indicate the better length estimate. Similarly, if the type242and subtype243values are not precisely known, then different values may be used and again the selection with the highest correlation in step1222used.

If, at steps1024,1114,1212and1226, the packet is “received”, an acknowledgement ACK packet is sent, such as via RF transmitter911, to the target station110, e.g., the Wi-Fi station.

FIG.13is another flowchart of an exemplary process1300for creating a corrected packet based in part on the majority vote. The exemplary process1300may be implemented in a first wireless device (WD) that supports wireless communication with a second WD. At step1301, a plurality of wireless packets is received from the second WD including at least a first wireless packet. At least another wireless packet of the plurality of wireless packets is one of a retry packet and a repeat packet of the first packet. Each wireless packet of the plurality of wireless packets comprises a plurality of bits and a first group of bits of the plurality of bits.

For each received wireless packet of the plurality of wireless packets, at step1302, the plurality of bits corresponding to the received wireless packet is demodulated, and, at step1303, the first group of bits is correlated with a predetermined group of bits. At step1304, a majority vote is performed based at least in part on the correlation of the first group of bits of each received wireless packet. At step1305, a corrected packet is created based in part on the majority vote.

Demodulating as used in the present disclosure may include determining and/or extracting information from a signal, e.g., determining/extracting information from a signal including a plurality of bits. In some embodiments, demodulating may include de-spreading, as described in the present disclosure, e.g., de-spreading at least one bit from a plurality of bits of a signal such as a signal that includes spread bits. In some other embodiments, demodulating may include de-scrambling, as described in the present disclosure, e.g., de-scrambling at least one bit from a plurality of bits of a signal such as a signal that includes scrambled bits. Although demodulating may include de-spreading and/or de-scrambling, demodulating is not limited to including de-spreading and/or de-scrambling and may include other steps/features described in the present disclosure.

The following is a nonlimiting list of embodiments according to the principles of the present disclosure:

Embodiment 1. A method in a first wireless device WD for the correction of wireless packets received with bit errors, the method comprising:

receiving a plurality of bit streams, transmitted from a second WD, of a repeated or re-tried wireless packet, each with bit errors, the wireless packet comprising:a portion A of the bit stream that is known a priori, anda portion B of the bit stream that is unknown; and

for each received packet:demodulating the received bit stream corresponding to the received packet;correlating portion A, with the known bit stream;determining that the correlation exceeds a set threshold;storing the received bit stream corresponding to the received packet in a store C;determining that there are an odd number, greater than 1, of stored received bit streams;performing a majority vote on each corresponding bit of each stored bit stream;re-creating a “corrected” bit stream using the results of the majority count and the portion A; andchecking whether the re-created “corrected” bit stream is error free.

Embodiment 2. The method of Embodiment 1, wherein the received bit stream is an IEEE 802.11 direct sequence spread spectrum (DSSS) where:

portion A comprises the de-spread, scrambled bits of the PHY Preamble field, PHY Header field and the medium access control, MAC Header up to the Sequence Control;

portion B comprises de-spread, scrambled bits of the Sequence control, frame body and frame check sum FCS fields.

Embodiment 3. The method of Embodiment 2 wherein:

the de-spread scrambled bit stream is stored in a store A; and

the de-spread de-scrambled bit stream is stored in a store B.

Embodiment 4. The method of Embodiment 3, wherein the value of the Length field in the PHY header is determined by one of the following methods:

checking the CRC value of the de-spread, scrambled PHY header bits, in store B, and if correct, saving the Length value;

if the CRC is not correct and the (known) values of the Signal and/or Service fields are incorrect:correcting the values of the Service and Signal fields:re-checking the CRC value of the corrected de-spread, scrambled PHY header bits, and, if correct, saving the Length value;or;

counting the number of bits stored in store A and estimating the value of the Length field based upon that count, and calculating a CRC value using that estimation.

Embodiment 5. The method of Embodiment 4, wherein the values for the following fields are set:

Duration field value is set to 314;

Retry bit is set to a 0 for the first received packet and the set to 1 for any subsequent, retired packets; and

Type and Subtype fields are set to correspond to the expected or desired packet type.

Embodiment 6. The method of Embodiment 5, wherein:

calculating the initial 368 scrambled bits of the error free version of the received bit stream, comprising:known a priori values of the PHY preamble;known a priori values of the Signal field, and the Service field;determined or estimated values of the Length field and CRC;Frame control field, assuming values for the Duration field, Type and subtype fields; andknown a priori Address 1, Address 2 and Address 3 fields;

auto-correlating the initial 368 calculated scrambled bits of the error free version of the received bit stream, with the first 368 bits of the received bit stream (store A);

determining that a correlation threshold has been exceeded;

storing the received bit stream in store C;

determining that there are an odd number, greater than 1, of stored received bit streams in store C;

performing a majority vote on each corresponding bit of each stored bit stream (store C);

re-creating a “corrected” bit stream using the results of the majority count and the initial 368 scrambled bits of the error free version of the received bit stream;

performing a check on the FCS value of the re-created “corrected” bit stream; and if correct; and

determining that the packet has been received correctly.

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.

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 choices of correlation thresholds, the number of stores, the number of trials for the majority voting, the number of bits used for the auto-correlation, the number of maximum retries, the value of a timeout timer, the method of measuring the Length field. Accordingly, the scope should be determined not by the embodiments illustrated, but by the claims and their legal equivalents.

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 of the following claims.