# Patent

## Title
System and method for received channel power indicator (RCPI) measurement

## Abstract

A received channel power indicator (RCPI) value is used as a measure of the received RF power in the selected channel, measured at the antenna connector. This parameter is a measure by the PHY sublayer of the received RF power in the channel measured over the PLCP preamble and over the entire received frame. RCPI is a monotonically increasing, logarithmic function of the received power level defined in dBm.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a continuation of U.S. patent application Ser. No. 10/799,974 filed Mar. 12, 2004, now U.S. Pat. No. 7,668,132, which claims the benefit of U.S. provisional application No. 60/454,375 filed Mar. 12, 2003, U.S. provisional application No. 60/465,024 filed Apr. 23, 2003, and U.S. provisional application No. 60/507,686 filed Sep. 30, 2003, all of which are hereby incorporated by reference.


FIELD OF INVENTION
The present invention relates to wireless communications systems, and more particularly, to a system and method for measuring a received channel power indicator (RCPI).
BACKGROUND
A received signal strength indicator (RSSI) is defined at the antenna input connector, but it is not fully specified, because there are no unit definitions and no performance requirements, such as accuracy or testability. It is not possible to extract meaning from a comparison of RSSIs from different stations and from different channels/physical layers (PHYs) within the same station. RSSI may have limited use for evaluating access point (AP) options within a station, such as a wireless local area network (WLAN) station, and within a given PHY, but is not useful for evaluations between PHYs. RSSI is rescaled between direct sequence spread spectrum (DSSS) and orthogonal frequency division multiplex (OFDM) PHYs. RSSI is clearly not useable by network management for handoff or load balancing. RSSI from one station does not relate to RSSI from any other station. In high interference environments, RSSI is not an adequate indicator of desired signal quality, since it indicates the sum of:
desired signal+noise+interference powers.
SUMMARY
A receiver analyses a signal in order to obtain a received channel power indicator (RCPI) value. The RCPI value is a measure of the received radio frequency (RF) power in the selected channel, measured at the antenna connector. This parameter is a measure by the PHY sublayer of the received RF power in the channel measured over the physical layer convergence protocol (PLCP) preamble and over the entire received frame. RCPI is a monotonically increasing, logarithmic function of the received power level defined in dBm.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a system employing RCPI and PSNI according to the present invention.
FIGS. 2A and 2B are diagrams showing examples of RCPI and PSNI measurements.
FIG. 3 shows RCPI and PSNI in relation to SNR in the demodulator.
FIG. 4 is a graph showing PSNI value versus BER.
FIG. 5 is a diagram of a first PLCP.
FIG. 6 is a diagram of a second PLCP.
FIG. 7 is a diagram of a third PLCP.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A received channel power indicator (RCPI) disclosed herein provides a quantized, objective input power measure (S+N+I), wherein S is the signal power, N is the noise power, and I is the interference power. A perceived signal to noise indicator (PSNI) provides a value which is a measure of the perceived, post-processing signal-to-noise-plus-interference (S/(N+I)) ratio in the demodulator. The PSNI provides a quantized, comparative measure of received signal quality [observed S/(N+I)] for all channels/rates and among all PHYs and between all stations.
FIG. 1 is a block diagram of a system 11 employing RCPI and PSNI according to the present invention. The system 11 includes a front end 12, an analog-digital converter 13, and a PHY specific demodulator and tracking loops module 14. The front end 12, an analog-digital converter 13, and a PHY specific demodulator and tracking loops module 14 form an AGC section 15. Also shown is an optional FEC decoder 17 and a frame check module 18. The system 11 resolves an incoming signal in a plurality of stages, shown as A through E. The RCPI according to the present invention measures total radio frequency (RF) power A at an antenna input 21. This is the total RF power, measured as RF S/(N+I) for each AP. The output of the front end 12, represented at B, is BB S/(N+I) for each AP, where BB is a power constant used by the AGC 15. The output of the demodulator and tracking loops 14, which also corresponds to the output of the FEC decoder 17, is the bit error rate (BER) for each data rate from each AP. The output of the frame check module 18 is the frame error rate (FER) for each data rate from each AP. The PSNI measures observed S/(N+I) within a demodulator but normalizes measurement for the FER at output E.
FIGS. 2A and 2B are diagrams showing examples of RCPI and PSNI measurements at different stations 31-33. The measurements at FIG. 2A correspond to measured RCPI power at A (FIG. 1). The signal is measured at the same objective SNR for the different stations 31-33. The measurements at FIG. 2B correspond to a measured PNSI quantity, used to determine FER at E (FIG. 1). The signal is measured at the same subjective SNR for the different stations 31-33. Although an accurate S/(N+I) measurement at A is somewhat useful, RF demodulation implementations vary widely from station to station, and the S/(N+1) measurement cannot be used comparatively between stations 31-33 to evaluate delivered signal quality. Accurate FER measurement at output E is an ideal quality measure, but cannot be measured frame by frame. FER can only be accurately measured over a large number of frames, typically several hundred to several thousand frames. Also, FERs are comparable only at the same frame size and data rate.
FIG. 3 shows RCPI and PSNI in relation to SNR in the demodulator. Starting with Boltzman's constant, a thermal input noise level and interference power at input appear at the antenna connector input (21, FIG. 1). The received channel power level is that signal, minus channel impairments, receive amp noise, demodulator loss, FEC decoder loss, and a combination of a theoretical SNR for required reception and operating margin. The level at the antenna connector input is either the input SNR ratio or the input analog SNIR, depending on whether interference power at input is included. The signal after channel impairments, receive amp noise, demodulator loss and FEC decoder loss is the observed digital SNIR, which is the PSNI in the demodulator. The PSNI in the demodulator, when combined with the theoretical SNR for required reception, or the SNR for required reception plus the operating margin, is the received channel power level desired.
FIG. 4 is a graph showing PSNI value versus BER.
The present invention measures input power RCPI, which is preferably specified in a manner similar to RSSI, for example by an eight (8) bit unsigned value, monotonically increasing with increasing signal strength. In one preferred embodiment, RCPI is logarithmically scaled in dB to measure the total received power within the defined channel bandwidth at the antenna connector A (see FIG. 1), and includes power from the desired signal, noise and interference. RCPI values are quantified in dBm and accuracy is specified across the entire RCPI range. The 221 RCPI levels range from −110 dBm to 0 dBm with 2 units per dB. RCPI accuracy is +/−5 dB across the defined range, equivalent to accuracy specified by TGH for the RPI histogram. RCPI may be used wherever RSSI is specified. The above makes the RCPI value highly desirable and broadly applicable as a frame quality measurement useful for all PHYs and STAs. It is noted that the use of the RCPI provides ease of implementation with modern manufacturers and paves the way for advanced antenna designs.
The RCPI value is a measure of the received RF power in the selected channel, measured at the antenna connector A. This parameter is a measure by the PHY sublayer of the received RF power in the channel measured over the PLCP preamble and over the entire received frame. RCPI is a monotonically increasing, logarithmic function of the received power level defined in dBm. The allowed values for the RCPI parameter are an eight (8) bit value in the range from 0 through 220 (decimal), with indicated values rounded to the nearest 0.5 dB as follows:



  
    
      0
      ⁢
      
        :
      
      ⁢
      
        
      
      ⁢
      Power
    
    <
    
      
        -
        110
      
      ⁢
      
        
      
      ⁢
      dBm
    
  




  
    
      1
      ⁢
      
        :
      
      ⁢
      
        
      
      ⁢
      Power
    
    =
    
      
        -
        109.5
      
      ⁢
      
        
      
      ⁢
      dBm
    
  




  
    
      2
      ⁢
      
        :
      
      ⁢
      
        
      
      ⁢
      Power
    
    =
    
      
        -
        109.0
      
      ⁢
      
        
      
      ⁢
      dBm
    
  




  
    
      
    
    ⁢
    ⋮
  




  
    
      
    
    ⁢
    ⋮
  




  
    
      
    
    ⁢
    ⋮
  




  
    
      220
      ⁢
      
        :
      
      ⁢
      
        
      
      ⁢
      Power
    
    >
    
      
        -
        0
      
      ⁢
      
        
      
      ⁢
      dBm
    
  




  
    221
    ⁢
    
      -
    
    ⁢
    255
    ⁢
    
      :
    
    ⁢
    
      
    
    ⁢
    reserved
  



Accuracy for each measurement is +/−5 dB. The measurement assumes a receiver noise equivalent bandwidth of 22 MHz.
The perceived signal to noise plus interference (PSNI) indicator is a demodulator specific, post-processing estimation of observed S/(N+I) and BER/FER. All digital demodulators use tracking loops and complex post-processing to demodulate received symbols. Many internal demodulator metrics are proportional to perceived S/(N+I). Some examples include:
phase shift keying (PSK): baseband phase jitter and received error vector magnitude (EVM)
DSSS: spreading code correlation quality
OFDM: frequency tracking and channel tracking stability
Demodulator internal metrics are available on a frame-by-frame basis. Demodulator metrics proportional to S/(N+I) are available at all data rates. Demodulator internal metrics may be calibrated with respect to actual FER performance to accurately indicate perceived or observed S/(N+I) in a controlled environment with additive white Gaussian noise (AWGN). Such demodulator internal metrics provide fast estimations of S/(N+I) in both interference environments and interference-free (noise only) environments. In one potential implementation of IEE 802.11, called Task Group K of 802.11 (TGK), it is not necessary to specify which demodulator metrics to use, but it is only necessary to specify how the quantized PSNI indicator relates to S/(N+I) and FER. For example, TGK may specify that for STAs which comply with 802.11k, STAs may report RCPI (or PSNI) in any data field calling for RSSI. A new station management entity (SME) control variable could specify the use of the RSSI field: a) for RCPI, b) for PSNI (perceived signal to noise indication), or c) for RSSI.
One preferred embodiment of the present invention measures output signal quality to obtain PSNI. PSNI is specified like RSSI: an eight-bit unsigned value, monotonically increasing with increasing S/(N+I). PSNI is logarithmically scaled to perceived S/(N+I) which relates directly to FER performance. A PSNI output value is specified for each data rate using FER points: a first point to an “anchor” indicator, and additional points to quantize and scale the indicator slope and the range of values. Accuracy of the PSNI in AWGN is specified to be +/−1 dB for all FER points. PSNI range spans the lower 32 dB portion of the operating range of S/(N+I) to cover high FERs at data rates from 1 to 54 Mbps.
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 PSNI parameter are an eight (8) bit value in the range from 0 through 255 (decimal). This parameter is a measure by the PHY sublayer of the perceived signal quality observed after RF downconversion to baseband, and is derived from internal digital signal processing metrics of the 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). PSNI accuracy and range are specified in additive white Gaussian noise (AWGN) at given FERs for each data rate as depicted in Table 1.
Theoretical FEC coding gain assumed in FER calculations is given by:

R=1/2, 5.4 dB gain

R=2/3, 4.7 dB gain

R=3/4, 4.4 dB gain

The PSNI special value of zero indicates an inability to measure PSNI. When PSNI exceeds the high end of the measurable range for a given data rate, the maximum PSNI for that rate is reported.
The data rate/modulation (DRM) adjustments used to offset BER curves are as depicted in Table 2.
Table 3 shows the values obtained for Eb/No, BER, and FER for a PSNI=101. Bit error rates (BERs) vary based on the forward error correction (FEC) coding used at each data rate. FERs vary based on BER and PPDU length. Note that for any station, PSNI will vary only as a result of changing channel conditions or changing received desired signal power level. Note that for efficiency, all stations preferably operate at the highest data rate possible while maintaining an acceptable FER (QoS).
Analyzing PSNI in relation to observed Eb/No, a PSNI value of zero is selected for a post-processing, observed Eb/No (OEbNo) equal to 4.4 dB, for binary phase shift keying (BPSK) at 1 Mbit/s data rate. Eight units (steps) per dB is selected to provide a 32 dB range in an eight-bit PSNI value. For 1 Mbit/s BPSK operation, PSNI=8*[OEbNo−4.4 dB]. In general, for all other data rates and modulations:

PSNI=8*[OEbNo−4.4 dB+DRMx−CFy]  Equation (1)

where DRMx is an S/N adjustment unique for each data rate/demodulation combination. DRM values are calculated in Table 1. CFy is a hardware-specific factor used to account for implementation variances in each FEC decoder in the station. CFy=CGtheo−CGact=actual FEC decoder loss, for each decoder at each specified FER point. CGtheo represents theoretical coding gain and CGact represents actual coding gain. CGtheo values are listed in Table 1. When no FEC decoder is used, CFy=0. Equation 1 is the foundation of the PSNI measurement.
Analyzing PSNI in relation to input signal to noise plus interference ratio (ISNIR) as follows:




  
    
      
        
          
        
        ⁢
        
          
            SNR
            =
            
              C
              /
              N
            
          
          ,
          
            
              where
              ⁢
              
                
              
              ⁢
              Eb
            
            =
            
              C
              *
              Tb
            
          
          ,
          
            

          
          ⁢
          
            
          
          ⁢
          
            N
            =
            
              
                No
                *
                NBW
                ⁢
                
                  
                
                ⁢
                
                  (
                  
                    noise
                    ⁢
                    
                      
                    
                    ⁢
                    BW
                  
                  )
                
                ⁢
                
                  
                
                ⁢
                and
                ⁢
                
                  
                
                ⁢
                DR
              
              =
              
                1
                /
                
                  Tb
                  .
                  
                    

                  
                  ⁢
                  
                    
                  
                  ⁢
                  Thus
                
              
            
          
          ,
        
      
    
    
      
        
      
    
  
  
    
      
        
          
        
        ⁢
        
          
            
              
                SNR
                =
                
                ⁢
                
                  
                    EB
                    /
                    Tb
                  
                  
                    No
                    *
                    NBW
                  
                
              
            
          
          
            
              
                =
                
                ⁢
                
                  
                    Eb
                    *
                    DR
                  
                  
                    No
                    *
                    NBW
                  
                
              
            
          
          
            
              
                =
                
                ⁢
                
                  EbNo
                  *
                  
                    DR
                    /
                    NBW
                  
                
              
            
          
        
      
    
    
      
        Equation
        ⁢
        
          
        
        ⁢
        
          (
          2
          )
        
      
    
  
  
    
      
        
          
        
        ⁢
        
          
            
              In
              ⁢
              
                
              
              ⁢
              db
              ⁢
              
                :
              
              ⁢
              
                
              
              ⁢
              SNR
            
            =
            
              EbNo
              +
              DR
              -
              NBW
            
          
          ⁢
          
            

          
          ⁢
          
            
          
          ⁢
          
            
              
                For
                ⁢
                
                  
                
                ⁢
                DR
              
              =
              
                
                  1
                  ⁢
                  
                    
                  
                  ⁢
                  Mbits
                  ⁢
                  
                    /
                  
                  ⁢
                  s
                  ⁢
                  
                    
                  
                  ⁢
                  and
                  ⁢
                  
                    
                  
                  ⁢
                  NBW
                
                =
                
                  22
                  ⁢
                  
                    
                  
                  ⁢
                  MHz
                
              
            
            ,
          
        
      
    
    
      
        Equation
        ⁢
        
          
        
        ⁢
        
          (
          
            3
            ⁢
            a
          
          )
        
      
    
  
  
    
      
        
          
        
        ⁢
        
          
            
              
                
                  SNR
                  =
                  
                  ⁢
                  
                    EbNo
                    +
                    
                      60
                      ⁢
                      
                        
                      
                      ⁢
                      dB
                    
                    -
                    
                      73.4
                      ⁢
                      
                        
                      
                      ⁢
                      dB
                    
                  
                
              
            
            
              
                
                  =
                  
                  ⁢
                  
                    EbNo
                    -
                    
                      13.4
                      ⁢
                      
                        
                      
                      ⁢
                      dB
                    
                  
                
              
            
          
          ⁢
          
            

          
          ⁢
          
            
          
          ⁢
          
            
              In
              ⁢
              
                
              
              ⁢
              general
            
            ,
          
        
      
    
    
      
        Equation
        ⁢
        
          
        
        ⁢
        
          (
          
            3
            ⁢
            b
          
          )
        
      
    
  
  
    
      
        
          
        
        ⁢
        
          
            
              SNR
              =
              
                EbNo
                -
                
                  13.4
                  ⁢
                  
                    
                  
                  ⁢
                  dB
                  ⁢
                  
                    
                  
                  ⁢
                  DRMx
                
              
            
            ,
            
              

            
            ⁢
            
              
            
            ⁢
            
              with
              ⁢
              
                
              
              ⁢
              DRMx
              ⁢
              
                
              
              ⁢
              from
              ⁢
              
                
              
              ⁢
              Table
              ⁢
              
                
              
              ⁢
              1.
            
          
          ⁢
          
            

          
          ⁢
          
            
          
          ⁢
          
            Therefore
            ,
          
        
      
    
    
      
        Equation
        ⁢
        
          
        
        ⁢
        
          (
          4
          )
        
      
    
  
  
    
      
        
          
        
        ⁢
        
          
            EbNo
            =
            
              SNR
              +
              
                13.4
                ⁢
                
                  
                
                ⁢
                dB
              
              -
              DRMx
            
          
          ⁢
          
            

          
          ⁢
          
            
          
          ⁢
          and
        
      
    
    
      
        Equation
        ⁢
        
          
        
        ⁢
        
          (
          
            5
            ⁢
            a
          
          )
        
      
    
  
  
    
      
        
          
        
        ⁢
        
          
            OEbNo
            =
            
              OSNIR
              +
              
                13.4
                ⁢
                
                  
                
                ⁢
                dB
              
              -
              DRMx
            
          
          ⁢
          
            

          
          ⁢
          
            
          
          ⁢
          
            
              Employing
              ⁢
              
                
              
              ⁢
              Equation
              ⁢
              
                
              
              ⁢
              1
            
            ,
            
              i
              .
              e
              .
            
            ,
            
              

            
            ⁢
            
              
            
            ⁢
            
              PSNI
              =
              
                8
                *
                
                  [
                  
                    OEbNo
                    -
                    
                      4.4
                      ⁢
                      
                        
                      
                      ⁢
                      dB
                    
                    +
                    DRMx
                    -
                    CFy
                  
                  ]
                
              
            
            ,
            
              

            
            ⁢
            
              
            
            ⁢
            
              and
              ⁢
              
                
              
              ⁢
              substituting
              ⁢
              
                
              
              ⁢
              for
              ⁢
              
                
              
              ⁢
              OEbNo
            
            ,
            
              

            
            ⁢
            
              PSNI
              =
              
                8
                *
                
                  [
                  
                    
                      (
                      
                        OSNIR
                        +
                        
                          13.4
                          ⁢
                          
                            
                          
                          ⁢
                          dB
                        
                        -
                        DRMx
                      
                      )
                    
                    -
                    
                      4.4
                      ⁢
                      
                        
                      
                      ⁢
                      dB
                    
                    +
                    DRMx
                    -
                    CFy
                  
                  ]
                
              
            
            ,
            
              

            
            ⁢
            
              
            
            ⁢
            
              
                and
                ⁢
                
                  
                
                ⁢
                PSNI
              
              =
              
                8
                *
                
                  
                    [
                    
                      OSNIR
                      +
                      
                        9.0
                        ⁢
                        
                          
                        
                        ⁢
                        dB
                      
                      -
                      CFy
                    
                    ]
                  
                  .
                  
                    
                  
                  ⁢
                  Since
                
              
            
          
        
      
    
    
      
        Equation
        ⁢
        
          
        
        ⁢
        
          (
          
            5
            ⁢
            b
          
          )
        
      
    
  
  
    
      
        
          
        
        ⁢
        
          
            ISNIR
            =
            
              OSNIR
              +
              TML
              +
              CI
            
          
          ,
        
      
    
    
      
        Equation
        ⁢
        
          
        
        ⁢
        
          (
          6
          )
        
      
    
  




where TML is the modem implementation loss and CI is the sum of all channel impairments, we have

PSNI=8*[(ISNIR−TML−CI)+9.0 dB−CFy]  Equation (7)

Analyzing PSNI in relation to BER/FER, PSNI is a direct measure of observed SNIR considering all channel impairments and implementation losses measured at the demodulator. PSNI is specified with respect to output FER, which considers all implementation losses including any FEC decoder implementation loss. Each station measures PSNI using a correction factor CFy to account for the actual coding gain (CGact) of each FEC decoder. Any station measuring PSNI on a frame using FEC will use CFy so that the reported PSNI from all stations is normalized and assumes a theoretical coding gain.

CFy=CGtheo−CGact=actual FEC decoder loss.  Equation (8)

Reported PSNI value may be used to estimate OEbNo and BER/FER (QOS) for the reporting station for each data rate.

OEbNo=(PSNI/8)+4.4 dB−DRMx  Equation (9)

For data rates without an FEC decoder, OEbNo is used with the theoretical PSK EbNo curve to estimate BER. For data rates with an FEC decoder, OEbNo is used with the theoretical FEC EbNo curve for PSK to estimate BER. Note that the PSNI relationship to BER is specified only for AWGN. Since the net effect of channel impairments is to degrade OEbNo in the same way as AWGN, PSNI should be an adequate estimator of BER in all channel conditions.
PHY-RXSTART.Indication (Physical Layer-Receive Start Indication)
This is an indication by the PHY to the local medium access control (MAC) entity that the PLCP has received a valid start frame delimiter (SFD) and PLCP Header. The primitive provides the following parameter: PHY-RXSTART.indication (RXVECTOR).
The RXVECTOR represents a list of parameters that the PHY provides the local MAC entity upon receipt of a valid PLCP Header or upon receipt of the last PSDU data bit in the received frame. This vector contains both MAC and MAC management parameters. This primitive is generated by the local PHY entity to the MAC sublayer when the PHY has successfully validated the PLCP header error check (HEC) cyclic redundancy code (CRC) at the start of a new PLCP protocol data unit (PPDU). The effect of receipt of this primitive by the MAC is unspecified.
PHY-RXEND.Indication
This primitive is an indication by the PHY to the local MAC entity that the MPDU currently being received is complete. The primitive provides the following parameters: PHY-RXEND.indication (RXERROR, RXVECTOR). The RXERROR parameter can convey one or more of the following values: NoError, FormatViolation, CarrierLost, or UnsupportedRate. A number of error conditions may occur after the PLCP's receive state machine has detected what appears to be a valid preamble and SFD. The following describes the parameter returned for each of those error conditions.
NoError. This value is used to indicate that no error occurred during the receive process in the PLCP.
Format Violation. This value is used to indicate that the format of the received PPDU was in error.
CarrierLost. This value is used to indicate that during the reception of the incoming protocol data unit (MPDU), the carrier was lost and no further processing of the MPDU can be accomplished.
UnsupportedRate. This value is used to indicate that during the reception of the incoming PPDU, a nonsupported date rate was detected.
The RXVECTOR represents a list of parameters that the PHY provides the local MAC entity upon receipt of a valid PLCP Header or upon receipt of the last PSDU data bit in the received frame. This vector contains both MAC and MAC management parameters. This primitive is generated by the PHY for the local MAC entity to indicate that the receive state machine has completed a reception with or without errors. The effect of receipt of this primitive by the MAC is unspecified.
Receive PLCP
A first embodiment of a receive PLCP is shown in FIG. 5. In order to receive data, PHY-TXSTART.request is disabled so that the PHY entity is in the receive state. Further, through station management via the Physical Layer Management Entity (PLME), the PHY is set to the appropriate channel and the Clear Channel Assessment (CCA) method is chosen. Other receive parameters such as RSSI, RCPI, signal quality (SQ), and indicated data rate are accessed via the PHY-service access point (PHY-SAP), shown in Table 4.
Upon receiving the transmitted energy, according to the selected CCA mode, the physical layer medium—energy detection (PMD_ED) is enabled when the RSSI level crosses the ED_THRESHOLD and/or PMD_Carrier_Sense (PMD_CS) is enabled after code lock is established. These conditions are used to indicate activity to the MAC via PHY-CCA.indicate. PHY-CCA.indicate (BUSY) is issued for energy detection (ED) and/or code lock prior to correct reception of the PLCP frame. The PMD primitives PMD—signal quality (PMD_SQ) and PMD_RSSI are issued to update the RSSI and SQ parameters reported to the MAC.
After PHY-CCA.indicate is issued, the PHY entity begins searching for the Start of Frame Delimiter SFD field. Once the SFD field is detected, CRC-16 processing is initiated and the PLCP IEEE 802.11 SIGNAL, IEEE 802.11 SERVICE and LENGTH fields are received. The CRC-16 frame check sequence (FCS) is processed, and if the CRC-16 FCS check fails, the PHY receiver returns to the RX IDLE state. Should the status of CCA return to the IDLE state during reception prior to completion of the full PLCP processing, the PHY receiver returns to the RX IDLE state.
If the PLCP Header reception is successful (and the SIGNAL field is completely recognizable and supported), a PHY-RXSTART.indicate (RXVECTOR) is issued. The RXVECTOR associated with this primitive includes the SIGNAL field, the
SERVICE field, the—MAC Protocol Data Units (MPDU) length in bytes (calculated from the LENGTH field in microseconds), the antenna used for receive (RX_ANTENNA), RSSI, PSNI, and SQ.
PMD_RCPI.Indicate (RCPI).
This primitive is the measure of the channel power received by the DSSS PHY measured at the antenna connector, and is generated by the PMD sublayer, provides the received channel power indicator to the PLCP and MAC. The primitive includes the following parameter: PMD_RCPI.indicate (RCPI). The RCPI is a measure of the channel power received by the direct sequence spread spectrum PHY (DSSS PHY) as measured at the antenna connector. RCPI value indications of eight bits (221 levels) are supported. This primitive is generated by the PMD when the DSSS PHY is in the receive state. It is continuously available to the PLCP, which, in turn, provides the parameter to the MAC entity. This parameter is provided to the PLCP layer for information only. The RCPI may be used in conjunction with PSNI to measure input signal quality.
RXVECTOR RCPI
The allowed values for the RCPI parameter are in the range from 0 through 220 and is a measure by the PHY of the received channel power at the antenna connector. RCPI value indications of eight bits (221 levels) are supported. PSNI is measured during the reception of the PLCP preamble and over the entire received frame. The RCPI is measured in the same manner as described above.
A second embodiment of a receive PLCP is shown in FIG. 6. In order to receive data, PHY-TXSTART.request is disabled so that the PHY entity is in the receive state. Further, through station management (via the PLME) the PHY is set to the appropriate frequency. Other receive parameters, such as RSSI, RCPI, and indicated data rate, are accessed via the PHY-SAP as previously described.
PMD_RCPI.Indicate
This primitive, generated by the PMD sublayer, provides the received channel power indicator to the PLCP and MAC entity and provides the following parameter: PMD_RCPI.indicate (RCPI).
The RCPI is a measure of the channel power received by the DSSS PHY as measured at the antenna connector. RCPI value indications of eight bits (221 levels) are supported. This primitive is generated by the PMD when the DSSS PHY is in the receive state. It is continuously available to the PLCP, which, in turn, provides the parameter to the MAC entity. This parameter is provided to the PLCP layer for information only. The RCPI may be used in conjunction with PSNI to measure input signal quality.
Receive PLCP
The receive procedures for receivers configured to receive the mandatory and optional PLCPs, rates, and modulations are described herein. A receiver that supports this High Rate extension of the standard is capable of receiving 5.5 Mbit/s and 11 Mbit/s, in addition to 1 Mbit/s and 2 Mbit/s. If the PHY implements the Short Preamble option, it detects both Short and Long Preamble formats and indicates which type of preamble was received in the RXVECTOR. If the PHY implements the packet binary convolution code (PBCC) Modulation option, it detects either complementary code keying (CCK) or PBCC Modulations, as indicated in the SIGNAL field, and reports the type of modulation used in the RXVECTOR.
The receiver implements the CCA procedure, in which, upon receiving a PPDU, the receiver distinguishes between a long and short header format by the value of the SFD. The receiver demodulates a long PLCP header using BPSK at 1 Mbit/s. The receiver demodulates a short PLCP header using QPSK at 2 Mbit/s. The receiver uses the SIGNAL and SERVICE fields of the PLCP header to determine the data rate and modulation of the PSDU.
A third embodiment of a receive PLCP is shown in FIG. 7. In order to receive data, the PHY-TXSTART.request is disabled so that the PHY entity is in the receive state. Further, through station management via the PLME, the PHY is set to the appropriate channel and the CCA method chosen. Others receive parameters, such as RSSI, RCPI, SQ, and indicated data rate, are accessed via the PHY-SAP as described previously.
Upon receiving the transmitted energy, according to the selected CCA mode, the PMD_ED is enabled as the RSSI reaches the ED_THRESHOLD, and/or PMD_CS is enabled after code lock is established. These conditions are used to indicate activity to the MAC via PHY-CCA.indicate. PHY-CCA.indicate (BUSY) is issued for ED and/or code lock prior to correct reception of the PLCP header. The PMD primitives, PMD_SQ, PMD_RSSI, PMD_RCPI, are issued to update the RSSI, RCPI, and SQ parameters reported to the MAC.
After PHY-CCA.indicate is issued, the PHY entity begins searching for the SFD field. Once the SFD field is detected, CRC-16 processing is initiated and the PLCP SIGNAL, SERVICE, and LENGTH fields are received. The CRC-16 FCS is processed. If the CRC-16 FCS check fails, the PHY receiver returns to the RX IDLE state. If the status of CCA returns to the IDLE state during reception prior to completion of the full PLCP processing, the PHY receiver returns to the RX IDLE state.
If the PLCP header reception is successful (and the SIGNAL field is completely recognizable and supported), a PHY-RXSTART.indicate (RXVECTOR) is issued. The RXVECTOR associated with this primitive includes: the SIGNAL field; the SERVICE field; the PSDU length in octets (calculated from the LENGTH field in microseconds and the data rate in Mbit/s); RXPREAMBLE_TYPE (which is an enumerated type taking on values SHORTPREAMBLE or LONGPREAMBLE); and the antenna used for receive (RX_ANTENNA), RSSI, RCPI, and SQ.
PMD_PSNI.Indicate
following parameter:













Parameter
Associated primitive
Value
Description







RCPI
PMD_RCPI.indicate
8 bits of
The RCPI is a measure of




RCPI
the antenna connector





channel power received by





the High Rate PHY, as





defined above in paragraph





[0023].









This primitive is generated by the PMD when the High Rate PHY is in the receive state. It is continuously available to the PLCP, which, in turn, provides the parameter to the MAC entity. This parameter is provided to the PLCP layer for information only. The RCPI may be used in conjunction with PSNI to measure input signal quality. The RCPI is measured as described above.







TABLE 1







PSNI Accuracy and Range












Data Rate

FEC
PPDU Length




(Mbit/s)
Mode
Rate
(bytes)
FER
PSNI















1
DSSS
no FEC
125
10% ± 0.2%
 32 ± 8


2
DSSS
no FEC
1250
10% ± 0.2%
 66 ± 8


5.5
HRDSSS
no FEC
1250
10% ± 0.2%
101 ± 8


5.5
HRDSSS
1⁄2
1250
10% ± 0.2%
 58 ± 8


6
OFDM
1⁄2
1250
10% ± 0.2%
 61 ± 8


9
OFDM
3⁄4
1250
10% ± 0.2%
 83 ± 8


11
HRDSSS
no FEC
1250
10% ± 0.2%
125 ± 8


11
HRDSSS
1⁄2
1250
10% ± 0.2%
 82 ± 8


12
OFDM
1⁄2
1250
10% ± 0.2%
 85 ± 8


18
OFDM
3⁄4
1250
10% ± 0.2%
107 ± 8


24
OFDM
1⁄2
1250
10% ± 0.2%
141 ± 8


36
OFDM
3⁄4
1250
10% ± 0.2%
163 ± 8


48
OFDM
2⁄3
1250
10% ± 0.2%
206 ± 8


54
OFDM
3⁄4
1250
10% ± 0.2%
213 ± 8
















TABLE 2







Data Rate/Modulation (DRM) Adjustments














Data


FEC
Coded
Data

DRM:


rate


code
rate
rate adj.
Modulation
Total S/N


(Mbps)
Mode
Modulation
rate
(Mbps)
(db)
adj. (db)
adj.(db)

















1
DSSS
BPSK
none
1
0
0
0





(SF = 11)






2
DSSS
QPSK
none
2
3
0
3





(SF = 11)






5.5
DSSS
QPSK
none
5.5
7.4
0
7.4



11b

(SF = 16)






5.5
DSSS
QPSK
1⁄2
11
7.4
0
7.4



11b

(SF = 2)






6
OFDM
BPSK
1⁄2
12
7.78
0
7.78


9
OFDM
BPSK
3⁄4
12
9.54
0
9.54


11
DSSS
QPSK
1⁄2
11
10.41
0
10.41



11b

(SF = 1)






11
DSSS
QPSK
none
11
10.41
0
10.41



11b

(SF = 8)






12
OFDM
QPSK
1⁄2
24
10.79
0
10.79


18
OFDM
QPSK
3⁄4
24
12.55
0
12.55


22
DSSS
8PSK
2⁄3
33
13.42
0
13.42



11g

(SF = 1)






24
OFDM
16-QAM
1⁄2
48
13.8
3.98
17.78


33
DSSS
8PSK
2⁄3
49.5
15.19
0
15.19



11g

(SF = 1)






36
OFDM
16-QAM
3⁄4
48
15.56
3.98
19.54


48
OFDM
64-QAM
2⁄3
72
16.81
8.45
25.26


54
OFDM
64-QAM
3⁄4
72
17.32
8.45
25.77






















TABLE 3







Data Rate
Eb/No

PPDU




(Mbps)/FEC
(dB)
BER
Length
FER






















5.5 (none)
9.6
1.00E−05
1250
1.00E−01



5.5 (R = 1/2)
9.6
1.25E−13
1250
1.00E−09



  6 (R = 1⁄2)
9.2
1.25E−12
1250
1.00E−08



  9 (R = 3⁄4)
7.5
6.00E−09
1250
4.80E−05



 11 (none)
6.6
1.25E−03
10
1.00E−01



 11 (R = 1⁄2)
6.6
2.00E−09
12
2.00E−05



 12 (R = 1⁄2)
6.2
2.00E−08
1250
2.00E−04



 18 (R = 3⁄4)
4.4
1.40E−04
10
1.10E−02

















TABLE 4







PHY-SAP service primitive parameters









Parameter
Associated primitive
Value





DATA
PHY-DATA.request
Octet value X′00′-X′FF′



PHY-DATA.indication


TXVECTOR
PHY-TXSTART.request
A set of parameters


STATUS
PHY-CCA.indication
BUSY, IDLE


RXVECTOR
PHY-RXSTART.indication
A set of parameters



PHY-RXEND.indication


RXERROR
PHY-RXEND.indication
NoError, FormatViolation,




Carrier-Lost,




UnsupportedRate
















TABLE 5







PMD_SAP peer-to-peer service primitive parameters











Parameter
Associated primitive
Value







LENGTH
RXVECTOR,
0 to 2E13-1




TXVECTOR



DATARATE
RXVECTOR,
1.2 Mbit/s




TXVECTOR



SERVICE
RXVECTOR,
1.2 Mbit/s




TXVECTOR



TXPWR_LEVEL
TXVECTOR
1.2 Mbit/s



TX_ANTENNA
TXVECTOR
1.2 Mbit/s



RSSI
RXVECTOR
1.2 Mbit/s



RCPI
RXVECTOR
1.2 Mbit/s



SQ
RXVECTOR
1.2 Mbit/s



RX_ANTENNA
RXVECTOR
1.2 Mbit/s

















TABLE 6







PMD_SAP sublayer-to-sublayer service primitives











Primitive
Request
Indicate
Confirm
Response





PMD_TXSTART
X

—
—


PMD_TXEND
X
X
—
—


PMD_ANTSEL
X

—
—


PMD_TXPWRLEVL
X

—
—


PMD_RATE
X
X
—
—


PMD_RSSI

X
—
—


PMD_RCPI

X
—
—


PMD_SQ

X
—
—


PMD_CS

X
—
—


PMD_ED
X
X
—
—
















TABLE 7







PMD_SAP service primitive parameters










Associated



Parameter
Primitive
Value





DATA
PHY-DATA.request
Octet value: X′00′-X′FF′



PHY-DATA.indicate


TXVECTOR
PHY-DATA.request
A set of parameters


RXVECTOR
PHY-DATA.indicate
A set of parameters


TX_UNIT
PMD-DATA.request
1, 0: DBPSK




dibit combinations




00, 01, 11, 10: DQPSK


RX_UNIT
PMD-DATA.indicate
1, 0: DBPSK




dibit combinations




00, 01, 11, 10: DQPSK


RF_STATE
PMD_TXE.request
Receive, Transmit


ANT_STATE
PMD-ANTSEL.indicate
1 to 256



PMD-ANTSEL.request


TXPWR_LEVEL
PHY-TXSTART
0, 1, 2, 3 (max of 4




levels)


RATE
PMD-RATE.indicate
X′0A′ for 1 Mbit/s



PMD-RATE.request
DBPSK




X′14′ for 2 Mbit/s




DQPSK


RSSI
PMD-RSSI.indicate
0-8 bits of RSSI


RCPI
PMD-RCPI.indicate
8 bits of RCPI


SQ
PMD-SQ.indicate
0-8 bits of SQ
















TABLE 8







RXVECTOR parameters











Parameter
Associated primitive
Value







LENGTH
PHY-RXSTART.indicate
0 to 4095



RSSI
PHY-RXSTART.indicate
0 to RSSI maximum




(RXVECTOR)



RCPII
PHY-RXSTART.indicate
0 to 255




(RXVECTOR) PHY-




RXEND.indicate




(RXVECTOR)



DATARATE
PHY-RXSTART.request
6, 9, 12, 18, 24, 36,




(RXVECTOR)
48, 54



SERVICE
PHY-RXSTART.request
Null




(RXVECTOR)

















TABLE 9







PMD_SAP sublayer-to-sublayer service primitives











Primitive
Request
Indicate
Confirm
Response





PMD_TXSTART
X
—
—
—


PMD_TXEND
X
—
—
—


PMD_TXPWRLEVL
X
—
—
—


PMD_RATE
X
—
—
—


PMD_RSSI
—
X
—
—


PMD_RCPI
—
X
—
—
















TABLE 10







List of parameters for the PMD primitives









Parameter
Associated primitive
Value





TXD_UNIT
PMD-DATA.request
One(1), Zero(0): one




OFDM symbol value


RXD_UNIT
PMD-DATA.indicate
One(1), Zero(0): one




OFDM symbol value


TXPWR_LEVEL
PHY-TXSTART
1-8 (max of 8 levels)


RATE
PMD-RATE.request
12 Mbit/s (for BPSK)




24 Mbit/s (for QPSK)




48 Mbit/s (for 16-QAM)




72 Mbit/s (for 64-QAM)


RSSI
PMD-RSSI.indicate
0-8 bits of RSSI


RCPI
PMD-RCPI.indicate
8 bits of RCPI
















TABLE 11







Parameter vectors









Parameter
Associated vector
Value





DATARATE
RXVECTOR,
The rate used to transmit



TXVECTOR
the PSDU in Mbit/s.


LENGTH
RXVECTOR,
The length of the PSDU in



TXVECTOR
octets.


PREAMBLE_TYPE
RXVECTOR,
The preamble used for the



TXVECTOR
transmission of this PPDU.




This is an enumerated type




that can take the value




SHORTPREAMBLE or




LONGPREAMBLE.


MODULATION
RXVECTOR,
The modulation used for



TXVECTOR
the transmission of this




PSDU. This is an integer




where 0 means CCK and 1




means PBCC.


RX_ANTENNA
RXVECTOR
The antenna used for




receive.


RSSI
RXVECTOR
0-8 bits of RSSI


RCPI
RXVECTOR
8 bits of RCPI


SQ
RXVECTOR
0-8 bits of SQ
















TABLE 12







PMD_SAP sublayer-to-sublayer service primitives











Primitive
Request
Indicate
Confirm
Response





PMD_TXSTART
X
—
—
—


PMD_TXEND
X
—
—
—


PMD_PSNI
—
X
—
—


PMD_TXPWRLVL
X
—
—
—


PMD_MODULATION
X
X
—
—


PMD_PREAMBLE
X
X
—
—


PMD_RATE
X
X
—
—


PMD_RSSI
—
X
—
—


PMD_RCPI
—
X
—
—


PMD_SQ

X
—
—


PMD_CS

X
—
—


PMD_ED
X
X
—
—

## Claims

1. A method for receiving a received channel power indicator (RCPI) at an access point (AP), the method comprising:
transmitting a wireless signal to a wireless transmit receive unit (WTRU); and
receiving, from the WTRU, an RCPI parameter that is based on a measured radio frequency power measured over a data portion of a frame of the wireless signal at the WTRU, wherein the RCPI parameter is an 8-bit scalar value in a range between 0-220, wherein when the 8-bit scalar value is 0 , the RCPI parameter is less than −110 dBm, and when the 8-bit scalar value is 220 the RCPI parameter is greater than 0 dBm.

2. The method of claim 1 wherein the measured radio frequency power of the wireless signal is rounded to a nearest 0.5 dB.

3. The method of claim 1 wherein the measured radio frequency power of the wireless signal is measured to an accuracy of +/−5 dB.

4. A wireless access point (AP) comprising:
a transmitter configured to transmit a wireless signal to a wireless transmit receive unit (WTRU); and
a receiver configured to receive, from WTRU, a received channel power indicator (RCPI) parameter that is based on a measured radio frequency power measured over a data portion of a frame of the wireless signal at the WTRU, wherein the RCPI parameter is an 8-bit scalar value in a range between 0-220, wherein when the 8-bit scalar value is 0,the RCPI parameter is less than −110 dBm, and when the 8-bit scalar value is 220, the RCPI parameter is greater than 0 dBm.

5. The AP of claim 4 wherein the measured radio frequency power of the wireless signal is rounded to a nearest 0.5 dB.

6. The AP of claim 4 wherein the measured radio frequency power of the wireless signal is measured to an accuracy of +/−5 dB.

7. A wireless communication device comprising a Media Access Control (MAC) layer circuitry and a physical (PHY) layer circuitry, the PHY layer circuitry configured to:
measure a radio frequency power over a data portion of a frame of a received wireless signal; and
determine an 8-bit scalar value of a received channel power indicator (RCPI) parameter based on the radio frequency power, wherein the 8-bit scalar value is in a range between 0-220, and wherein when the 8-bit scalar value is 0, the RCPI parameter value is less than −110 dBm, and when the 8-bit scalar value is 220, the RCPI parameter is greater than 0 dBm.

8. The wireless communication device of claim 7, wherein the RCPI parameter is a monotonically increasing logarithmic function of the radio frequency power measured in dBm.

9. The wireless communication device of claim 7 wherein the PHY layer circuitry is configured to measure the radio frequency power over exactly one frame to generate the RCPI parameter, and wherein the RCPI parameter is not based on an average radio frequency power over a plurality of frames.

10. The wireless communication device of claim 7, wherein the 8 -bit scalar value of the RCPI parameter is provided in a PMD13RCPI primitive.

11. The wireless communication device of claim 7, wherein the PHY layer circuitry configured to measure the radio frequency power based on an automatic gain control (AGC) setting.

12. A wireless communication device comprising:
a circuitry configured to:
transmit a wireless signal to a wireless transmit receive unit (WTRU); and
receive, from the WTRU, a received channel power indicator (RCPI) parameter that is based on a measured radio frequency power measured over a data portion of a frame of the wireless signal at the WTRU, wherein the RCPI parameter is an 8-bit scalar value in a range between 0-220, wherein when the 8-bit scalar value is 0, the RCPI parameter s less than −110 dBm, and when the 8-bit scalar value is 220, the RCPI parameter is greater than 0 dBm.

13. The wireless communication device of claim 12, wherein the measured radio frequency power of the wireless signal is rounded to a nearest 0.5 dB.

14. The wireless communication device of claim 12, wherein the measured radio frequency power of the wireless signal is measured to an accuracy of +/−5 dB.

15. A user station (STA) comprising:
a receiver to receive a wireless signal from a wireless access point (AP); and
a circuitry configured to:
measure a radio frequency power over a data portion of a frame of the received wireless signal, and
determine an 8-bit scalar value of a received channel power indicator (RCPI) parameter based on the radio frequency power, wherein the 8-bit scalar value is in a range of 0-220, and wherein when the 8-bit scalar value is 0, the RCPI parameter is less than −110 dBm, and when the 8-bit scalar value is 220, the RCPI parameter is greater than 0 dBm; and

a transmitter to transmit the determined 8-bit scalar value of RCPI parameter to the wireless AP.

16. The STA of claim 15, wherein the circuitry is further configured to select an AP based on the determined 8-bit scalar value of RCPI parameter.

17. The STA of claim 15, further comprising:
one or more antenna connectors, and wherein the radio frequency power of the received signal is measured at the one or more antenna connectors.