Symbol error detection for bluetooth basic data rate packets
View Patent ↗A symbol error detector can be configured to detect symbol errors of GFSK modulated portions of a Bluetooth packet without relying solely on a CRC error detection mechanism. The symbol error detector can operate on frequency error signals that are a difference between a frequency associated with a current symbol and predetermined frequency outputs from a bank of filters matched to a frequency response of the Bluetooth receiver for predefined combinations of three consecutive symbols (i.e., an estimated previously decoded symbol, an estimated current symbol, and an estimated subsequent symbol). The frequency error signals can be compared against a threshold and against each other to determine a potential unreliability in decoding the current symbol and to determine whether to generate a symbol error notification. The frequency error signals being within a threshold of each other can indicate potential unreliability in decoding the current symbol.
1. A method comprising:
determining, at a receiver of a wireless network device, a frequency associated with a first symbol of a received signal, wherein the received signal comprises a plurality of symbols;
generating, at each of a plurality of filters matched to a frequency response of the receiver for a corresponding each of a plurality of predefined symbol combinations, a frequency output associated with each of the plurality of predefined symbol combinations;
calculating a frequency error, associated with each of the plurality of predefined symbol combinations, that indicates a difference between the frequency output associated with each of the plurality of predefined symbol combinations and the frequency associated with the first symbol of the received signal;
determining, based on comparing the frequency error associated with the each of the plurality of predefined symbol combinations, that a first frequency error associated with a first of the plurality of predefined symbol combinations is within a threshold of a second frequency error associated with a second of the plurality of predefined symbol combinations; and
generating a symbol error notification based on said determining that the first frequency error associated with the first of the plurality of predefined symbol combinations is within the threshold of the second frequency error associated with the second of the plurality of predefined symbol combinations.
2. The method of claim 1 , wherein said calculating the frequency error associated with each of the plurality of predefined symbol combinations that indicates the difference between the frequency output associated with each of the plurality of predefined symbol combinations and the frequency associated with the first symbol of the received signal, further comprises:
determining a squared magnitude of the difference between the frequency output associated with each of the plurality of predefined symbol combinations and the frequency associated with the first symbol of the received signal to yield the frequency error associated with each of the plurality of predefined symbol combinations, or
determining an absolute value of the difference between the frequency output associated with each of the plurality of predefined symbol combinations and the frequency associated with the first symbol of the received signal to yield the frequency error associated with each of the plurality of predefined symbol combinations.
3. The method of claim 1 , wherein said determining that the first frequency error associated with the first of the plurality of predefined symbol combinations is within the threshold of the second frequency error associated with the second of the plurality of predefined symbol combinations further comprises:
determining a ratio of the first frequency error associated with the first of the plurality of predefined symbol combinations and the second frequency error associated with the second of the plurality of predefined symbol combinations; and
comparing the ratio against the threshold for said determining that the frequency error associated with the first of the plurality of predefined symbol combinations is within the threshold of the frequency error associated with the second of the plurality of predefined symbol combinations.
4. The method of claim 1 , further comprising:
grouping the plurality of predefined symbol combinations to form a plurality of symbol groups, wherein each of the plurality of predefined symbol combinations comprises an estimated previously decoded symbol, an estimated current symbol, and an estimated subsequent symbol, wherein a subset of the plurality of predefined symbol combinations that constitute each of the plurality of symbol groups differ only in the estimated subsequent symbol;
for each of the plurality of symbol groups, comparing frequency errors associated with the subset of the plurality of predefined symbol combinations that constitute each of the plurality of symbol groups to identify a minimum frequency error associated with each of the plurality of symbol groups;
in response to determining a previously decoded symbol, identifying a first and a second of the plurality of symbol groups that constitute predefined symbol combinations with the previously decoded symbol; and
determining a ratio of a first minimum frequency error associated with the first of the plurality of symbol groups and a second minimum frequency error associated with the second of the plurality of symbol groups, wherein the first minimum frequency error associated with the first of the plurality of symbol groups is the first frequency error associated with the first of the plurality of predefined symbol combinations and the second minimum frequency error associated with the second of the plurality of symbol groups is the second frequency error associated with the second of the plurality of predefined symbol combinations.
5. The method of claim 4 , wherein said determining that the first frequency error associated with the first of the plurality of predefined symbol combinations is within the threshold of the second frequency error associated with the second of the plurality of predefined symbol combinations further comprises:
comparing the ratio of the first minimum frequency error associated with the first of the plurality of symbol groups and the second minimum frequency error associated with the second of the plurality of symbol groups against the threshold.
6. The method of claim 5 , wherein said generating the symbol error notification is in response to determining that the ratio of the first minimum frequency error associated with the first of the plurality of symbol groups and the second minimum frequency error associated with the second of the plurality of symbol groups is less than the threshold.
7. The method of claim 4 , further comprising
determining that the first minimum frequency error associated with the first of the plurality of symbol groups is a smallest of the minimum frequency errors associated with each of the plurality of symbol groups;
determining that the first minimum frequency error associated with the first of the plurality of symbol groups corresponds to the first frequency error associated with the first of the plurality of predefined symbol combinations; and
decoding the first symbol of the received signal based on said determining that the first minimum frequency error associated with the first of the plurality of symbol groups corresponds to the first frequency error associated with the first of the plurality of predefined symbol combinations.
8. The method of claim 7 , wherein said decoding the first symbol of the received signal further comprises:
identifying the estimated current symbol from the first of the plurality of predefined symbol combinations based, at least in part, on said determining that the first minimum frequency error associated with the first of the plurality of symbol groups corresponds to the first frequency error associated with the first of the plurality of predefined symbol combinations; and
designating, as a decoded first symbol, the estimated current symbol identified from the first of the plurality of predefined symbol combinations.
9. The method of claim 1 , wherein said generating the symbol error notification further comprises:
determining a number of symbols between a current symbol error and a previously detected symbol error, wherein the current symbol error is associated with the first symbol of the received signal;
comparing the number of symbols between the current symbol error and the previously detected symbol error to a predetermined burst length threshold, wherein the predetermined burst length threshold indicates a minimum number of symbols between two consecutive symbol errors that will cause an erroneously demodulated symbol to be undetected; and
generating the symbol error notification in response to determining that the first frequency error associated with the first of the plurality of predefined symbol combinations is within the threshold of the second frequency error associated with the second of the plurality of predefined symbol combinations and that the number of symbols between the current symbol error and the previously detected symbol error is greater than the predetermined burst length threshold.
10. The method of claim 9 , further comprising discarding the first symbol based, at least in part, on determining that the first frequency error associated with the first of the plurality of predefined symbol combinations is within the threshold of the second frequency error associated with the second of the plurality of predefined symbol combinations and that the number of symbols between the current symbol error and the previously detected symbol error is greater than the predetermined burst length threshold.
11. The method of claim 1 , further comprising discarding the first symbol based, at least in part, on determining that the first frequency error associated with the first of the plurality of predefined symbol combinations is within the threshold of the second frequency error associated with the second of the plurality of predefined symbol combinations.
12. The method of claim 1 , wherein the plurality of symbols are modulated using a Gaussian frequency shift keying (GFSK) modulation scheme.
13. A wireless network device comprising:
a frequency detector operable to determine a frequency associated with a first symbol of a received signal, wherein the received signal comprises a plurality of symbols;
a matched filterbank comprising a plurality of filters matched to a frequency response of the wireless network device for a corresponding each of a plurality of predefined symbol combinations, the matched filterbank operable to generate, at each of the plurality of filters, a frequency output associated with each of the plurality of predefined symbol combinations;
a symbol error detector operable to:
calculate a frequency error, associated with each of the plurality of predefined symbol combinations, that indicates a difference between the frequency output associated with each of the plurality of predefined symbol combinations and the frequency associated with the first symbol of the received signal;
determine, based on comparing the frequency error associated with the each of the plurality of predefined symbol combinations, that a first frequency error associated with a first of the plurality of predefined symbol combinations is within a threshold of a second frequency error associated with a second of the plurality of predefined symbol combinations; and
generate a symbol error notification based on the symbol error detector determining that the first frequency error associated with the first of the plurality of predefined symbol combinations is within the threshold of the second frequency error associated with the second of the plurality of predefined symbol combinations.
14. The wireless network device of claim 13 , wherein the symbol error detector operable to determine that the first frequency error associated with the first of the plurality of predefined symbol combinations is within the threshold of the second frequency error associated with the second of the plurality of predefined symbol combinations further comprises the symbol error detector operable to:
determine a ratio of the first frequency error associated with the first of the plurality of predefined symbol combinations and the second frequency error associated with the second of the plurality of predefined symbol combinations; and
compare the ratio against the threshold for determining that the frequency error associated with the first of the plurality of predefined symbol combinations is within the threshold of the frequency error associated with the second of the plurality of predefined symbol combinations.
15. The wireless network device of claim 13 , wherein the symbol error detector is further operable to:
group the plurality of predefined symbol combinations to form a plurality of symbol groups, wherein each of the plurality of predefined symbol combinations comprises an estimated previously decoded symbol, an estimated current symbol, and an estimated subsequent symbol, wherein a subset of the plurality of predefined symbol combinations that constitute each of the plurality of symbol groups differ only in the estimated subsequent symbol;
for each of the plurality of symbol groups, compare frequency errors associated with the subset of the plurality of predefined symbol combinations that constitute each of the plurality of symbol groups to identify a minimum frequency error associated with each of the plurality of symbol groups;
in response to determining a previously decoded symbol, identify a first and a second of the plurality of symbol groups that constitute predefined symbol combinations with the previously decoded symbol; and
determine a ratio of a first minimum frequency error associated with the first of the plurality of symbol groups and a second minimum frequency error associated with the second of the plurality of symbol groups, wherein the first minimum frequency error associated with the first of the plurality of symbol groups is the first frequency error associated with the first of the plurality of predefined symbol combinations and the second minimum frequency error associated with the second of the plurality of symbol groups is the second frequency error associated with the second of the plurality of predefined symbol combinations.
16. The wireless network device of claim 15 , wherein the symbol error detector operable to determine that the first frequency error associated with the first of the plurality of predefined symbol combinations is within the threshold of the second frequency error associated with the second of the plurality of predefined symbol combinations further comprises the symbol error detector operable to:
compare the ratio of the first minimum frequency error associated with the first of the plurality of symbol groups and the second minimum frequency error associated with the second of the plurality of symbol groups against the threshold.
17. The wireless network device of claim 13 , wherein the symbol error detector operable to generate the symbol error notification further comprises the symbol error detector operable to:
determine a number of symbols between a current symbol error and a previously detected symbol error, wherein the current symbol error is associated with the first symbol of the received signal;
compare the number of symbols between the current symbol error and the previously detected symbol error to a predetermined burst length threshold, wherein the predetermined burst length threshold indicates a minimum number of symbols between two consecutive symbol errors that will cause an erroneously demodulated symbol to be undetected; and
generate the symbol error notification in response to the symbol error detector determining that the first frequency error associated with the first of the plurality of predefined symbol combinations is within the threshold of the second frequency error associated with the second of the plurality of predefined symbol combinations and that the number of symbols between the current symbol error and the previously detected symbol error is greater than the predetermined burst length threshold.
18. A non-transitory machine-readable storage media, having instructions stored therein, which, when executed by one or more processors causes the one or more processors to perform operations that comprise:
determining a frequency associated with a first symbol of a signal received at a receiver of a wireless network device, wherein the received signal comprises a plurality of symbols;
generating, at each of a plurality of filters matched to a frequency response of the receiver for a corresponding each of a plurality of predefined symbol combinations, a frequency output associated with each of the plurality of predefined symbol combinations;
calculating a frequency error, associated with each of the plurality of predefined symbol combinations, that indicates a difference between the frequency output associated with each of the plurality of predefined symbol combinations and the frequency associated with the first symbol of the received signal;
determining, based on comparing the frequency error associated with the each of the plurality of predefined symbol combinations, that a first frequency error associated with a first of the plurality of predefined symbol combinations is within a threshold of a second frequency error associated with a second of the plurality of predefined symbol combinations; and
generating a symbol error notification based on said determining that the first frequency error associated with the first of the plurality of predefined symbol combinations is within the threshold of the second frequency error associated with the second of the plurality of predefined symbol combinations.
19. The non-transitory machine-readable storage media of claim 18 , wherein said operation of determining that the first frequency error associated with the first of the plurality of predefined symbol combinations is within the threshold of the second frequency error associated with the second of the plurality of predefined symbol combinations further comprises:
determining a ratio of the first frequency error associated with the first of the plurality of predefined symbol combinations and the second frequency error associated with the second of the plurality of predefined symbol combinations; and
comparing the ratio against the threshold for said determining that the frequency error associated with the first of the plurality of predefined symbol combinations is within the threshold of the frequency error associated with the second of the plurality of predefined symbol combinations.
20. The non-transitory machine-readable storage media of claim 18 , wherein the operations further comprise:
grouping the plurality of predefined symbol combinations to form a plurality of symbol groups, wherein each of the plurality of predefined symbol combinations comprises an estimated previously decoded symbol, an estimated current symbol, and an estimated subsequent symbol, wherein a subset of the plurality of predefined symbol combinations that constitute each of the plurality of symbol groups differ only in the estimated subsequent symbol;
for each of the plurality of symbol groups, comparing frequency errors associated with the subset of the plurality of predefined symbol combinations that constitute each of the plurality of symbol groups to identify a minimum frequency error associated with each of the plurality of symbol groups;
in response to determining a previously decoded symbol, identifying a first and a second of the plurality of symbol groups that constitute predefined symbol combinations with the previously decoded symbol; and
determining a ratio of a first minimum frequency error associated with the first of the plurality of symbol groups and a second minimum frequency error associated with the second of the plurality of symbol groups, wherein the first minimum frequency error associated with the first of the plurality of symbol groups is the first frequency error associated with the first of the plurality of predefined symbol combinations and the second minimum frequency error associated with the second of the plurality of symbol groups is the second frequency error associated with the second of the plurality of predefined symbol combinations.
21. The non-transitory machine-readable storage media of claim 20 , wherein said operation of determining that the first frequency error associated with the first of the plurality of predefined symbol combinations is within the threshold of the second frequency error associated with the second of the plurality of predefined symbol combinations further comprises:
comparing the ratio of the first minimum frequency error associated with the first of the plurality of symbol groups and the second minimum frequency error associated with the second of the plurality of symbol groups against the threshold.
22. The non-transitory machine-readable storage media of claim 18 , wherein said operation of generating the symbol error notification further comprises:
determining a number of symbols between a current symbol error and a previously detected symbol error, wherein the current symbol error is associated with the first symbol of the received signal;
comparing the number of symbols between the current symbol error and the previously detected symbol error to a predetermined burst length threshold, wherein the predetermined burst length threshold indicates a minimum number of symbols between two consecutive symbol errors that will cause an erroneously demodulated symbol to be undetected; and
generating the symbol error notification in response to determining that the first frequency error associated with the first of the plurality of predefined symbol combinations is within the threshold of the second frequency error associated with the second of the plurality of predefined symbol combinations and that the number of symbols between the current symbol error and the previously detected symbol error is greater than the predetermined burst length threshold.