Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
  • H04L1/0045—Arrangements at the receiver end
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B17/00—Monitoring; Testing
  • H04B17/30—Monitoring; Testing of propagation channels
  • H04B17/309—Measuring or estimating channel quality parameters
  • H04B17/318—Received signal strength
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B17/00—Monitoring; Testing
  • H04B17/30—Monitoring; Testing of propagation channels
  • H04B17/309—Measuring or estimating channel quality parameters
  • H04B17/336—Signal-to-interference ratio [SIR] or carrier-to-interference ratio [CIR]
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/20—Arrangements for detecting or preventing errors in the information received using signal quality detector
  • H04L1/203—Details of error rate determination, e.g. BER, FER or WER
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/20—Arrangements for detecting or preventing errors in the information received using signal quality detector
  • H04L1/205—Arrangements for detecting or preventing errors in the information received using signal quality detector jitter monitoring
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/20—Arrangements for detecting or preventing errors in the information received using signal quality detector
  • H04L1/206—Arrangements for detecting or preventing errors in the information received using signal quality detector for modulated signals

Definitions

• the present invention relates generally to network management, and more particularly to facilitating network management using a parameter of an observed signal obtained at a receiving location, which parameter serves as a perceived signal to noise (and interference) indicator (PSNI).
• PSNI perceived signal to noise (and interference) indicator
• the current IEEE standard 802.11 is entrusted with the task of providing interfaces, measurements, and mechanisms to support higher layer functions for efficient network management.
• the 802.11 standard has defined several physical parameters, none of which is completely suitable for network management purposes.
• One example of a measurable parameter is received signal strength indicator (RSSI), which is a reportable parameter for each received frame but is not quantified in the standards, and is not fully specified.
• RSSI received signal strength indicator
• the standards do include certain definitions in the context of RSSI, but it remains that RSSI poses certain limitations for use in network management since RSSI parameters from different stations (STAs) may not be uniformly defined and thus are not comparable.
• a second suggested measurable parameter is the signal quality
• RSSI as currently defined, only addresses categories (1) and (3) above.
• the RSSI is a measure of the RF energy received by the DSSS PHY or the
• RSSI indications of up to eight bits (256 levels) are supported.
• the allowed values for RSSI range from 0 through RSSI maximum. This parameter is a measure by the PHY sublayers of the energy observed at the antenna used to receive the current PPDU.
• RSSI is measured during the reception of the PLCP preamble. RSSI is intended to be used in a relative manner, and it is a monotonically increasing function of the received power.
• CCK, ER-PBCC the 8-bit value of RSSI as described in 18.4.5.11.
• ERP-OFDM DSSS-OFDM
• 8 bit value is in the range of 0 to
• RSSI is a monotonic, relative indicator of power at the antenna connector, which indicates sum of desired signal, noise, and interference powers. In high interference environments, RSSI is not an adequate indicator of desired signal quality. RSSI is not fully specified: there are no unit definitions and no performance requirements (accuracy, fidelity, testability). Since so little about RSSI is specified, it must be assumed that widely variant implementations already exist. It is not possible to compare RSSIs from different products and perhaps not even from different channels/bands within the same product.
• RSSI has limited use for evaluating AP options within a given PHY, it is not useful in comparing different PHYs. RSSI must be rescaled for DSSS and OFDM PHYs. RSSI is clearly not useable by network management for load balancing or load shifting and RSSI from one STA does not relate to RSSI from any other STA.
• the invention provides a network management method using a parameter of a signal which serves as perceived signal to noise indication (PSNI), in preference to RSSI which latter indication has several serious limitations.
• PSNI perceived signal to noise indication
• the allowed values for the PSNI parameter for example, may be in the range of 0 to 255.
• Figure 1 shows the options for PHY measurements
• Figure la is a flow diagram showing a technique for deriving an input to the FEC decoder
• Figure 2 shows PSNI specified on BER curves
• Figure 3 shows example PSNI specification points.
• DSSS spreading code correlation quality
• OFDM frequency tracking and channel tracking stability
• Demodulator internal parameters are available on a frame-by-frame basis. Demodulator parameters proportional to analog S/(N+I) are invariant with respect to data rates. The same parameter may be used at any data rate.
• Demodulator internal parameters may be specified and calibrated in a controlled environment with respect to actual FER performance at two or more operating points defined by rate, modulation, and FEC. Such demodulator internal parameters estimate FER performance in both interference environments and interference-free (noise only) environments and may be used as the basis for PSNI. For PSNI to be a useful indicator it is not necessary to specify which demodulator internal parameter to use as the basis for the indicator, but it is sufficient to only specify how the quantized indicator relates to FER.
• PSNI is specified like RSSI as an 8-bit unsigned value, monotonically increasing with increasing S/(N+I).
• PSNI is logarithmically scaled to perceived S/(N+I).
• PSNI is based on a demodulator internal parameter which provides a fast estimator for FER.
• PSNI range may span the lower 40 db portion of the operating range of S/(N+I) to cover high FERs at data rates from 1 to 54 Mbps, but higher or lower range spans may be used.
• the PSNI indicator is a measure of the perceived, post-processing signal-to-noise-plus-interference (S/(N+I)) ratio in the demodulator.
• the allowed values for the Perceived Signal to Noise Indicator (PSNI) parameter are in the range from 0 through 255 (i.e., eight binary bits). This parameter is a measure by the PHY sublayer of the perceived signal quality observed after RF downconversion, and is derived from internal digital signal processing parameters of a demodulator used to receive the current frame. PSNI is measured over the PLCP preamble and over the entire received frame. PSNI is intended to be used in a relative manner, and it is a monotonically increasing, logarithmic function of the observed S/(N+I).
• FIG. 1 shows the options for PHY measurements, which can be used for a PSNI indicator. Referring to the receiver 10 in Figure 1, the following general comments are valid for a wide range of modern modulation and coding techniques.
• the signal to noise ratio at points A and B are nominally the same and may differ slightly due to added losses in the radio front end 12.
• the signal to noise ratio after the analog to digital conversion at A/D converter 14 is also nominally the same value, with minor additions to the noise associated with quantization error.
• the BER at the output of FEC decoder 18 (point D) relates to the FEC decoder input according to a theoretical FEC decoder performance curve which is adjusted to account for actual FEC decoder implementation losses.
• the frame error rate (FER) at point E at the output of the frame check function 20 is a direct mathematical function of the BER and the error distribution statistics at point D. There are normally no implementation losses associated with the frame check. In general, for low BERs, the FER is equal to the BER multiplied by the frame size in bits.
• the frame check function 20 of receiver 10 in Figure 1 may be implemented with or without a frame parity check.
• each frame contains a parity check, which indicates (with high reliability) whether the block was received correctly or not.
• the most common parity check is a cyclic redundancy check (CRC), but other techniques are possible and acceptable.
• CRC cyclic redundancy check
• the FER may be estimated using a derived BER from the functioning of the FEC decoder 18. Deriving the BER input from the FEC decoder 18 may be obtained using a well known process, summarized as follows (see Fig. la):
• the output of the FEC decoder is generally correct. Therefore, this output is obtained and stored (steps SI and S2).
• the FEC encoding rules are used to create a replica of the correct input bits (step S3) and each bit is compared to the corresponding bit that was actually input to the FEC decoder and stored (step S4). A count is increased for each comparison (step S5).
• Each disagreement (step S6) represents an input bit error (step S7) which is accumulated.
• This derived BER (steps S9, S10) may then be used with the actual performance curve of the FEC decoder to estimate observed FER (step Sll).
• step S6 The comparisons (error or no error - step S6) are continued until a count N is reached (step S8), at which time the count at step S7 is identified as the BER (step S9).
• the signal quality delivered to the user is best represented by the actual FER or observed FER (point E).
• the PSNI concept provides an indicator which directly relates to observed FER for all STAs, regardless of each STA's different implementation loss. This is accomplished by 1) basing the PSNI on the measurement of an internal demodulator parameter, 2) specifying the PSNI indicator values with respect to observed FER at particular data rate/demodulation/FEC combination points, and 3) adjusting the internal demodulator parameter measurement to account for actual FEC decoder losses which occur downstream from the measurement point.
• the measured signal quality already includes the effects of the STA front end losses.
• actual demodulator losses are included.
• the validity of the indicator is preserved for all FEC decoders which the STA may use.
• PSNI is based on an internal demodulator parameter, it can be measured and reported on a frame-by-frame basis. BER or FER measurements at points C or E require thousands of frames for accurate measurement. Therefore PSNI is a practical, fast, and available indictor of observed signal quality.
• Measurements of analog signal to noise at points A or B can be performed quickly, yet without also knowing the sum of all the implementation losses further downstream, they cannot be accurately related to observed FER at point E.
• Figure 2 shows PSNI specified on BER curves in the context of the invention.
• Figure 3 illustrates example specification points for a PSNI scaled to a 43dB range.
• PSNI meets the requirements for RSSI in that the PSNI is an 8-bit unsigned value (for DSSS PHYs) and is proportional to received signal power.
• PSNI may be reported in any data field calling for RSSI, which makes the PSNI indicator broadly applicable as an interlayer frame quality measurement.
• MIB entries and reporting/posting may further be mandated in 802.11 to make the PSNI improvements available to higher layers.
• PSNI indicator and method of network management are applicable to all modes of transmission including TDD, FDD, CDMA, and other modes without exception. It is also conceivable that variations of the described PSNI indicator and method with suitable modifications are conceivable. All such modifications and variations are envisaged to be within the purview of the invention.

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• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Quality & Reliability (AREA)
• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Monitoring And Testing Of Transmission In General (AREA)
• Mobile Radio Communication Systems (AREA)
• Small-Scale Networks (AREA)
• Detection And Prevention Of Errors In Transmission (AREA)
• Data Exchanges In Wide-Area Networks (AREA)

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• 2003
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• 2004
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• 2007
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