1. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 1 CCK-OFDM Normative Text Summary Steve Halford Mark Webster Jim Zyren Intersil Corporation

2. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 2 CCK-OFDM Proposal: Modes CCK-OFDM at 6,12, & 24 Mbps is required 802.11a mode is optional Other CCK-OFDM rates are optional Mandatory Modes for TGg Systems Support all 802.11b mandatory functions Support CCK-OFDM at 6, 12, and 24 Mbps High Throughput Option Uses 802.11a Preamble Supports rates from 6 to 54 Mbps Not backward compatible to 802.11b 802.11a at 2.4 GHz High Rate Compatible Option CCK-OFDM at optional rates Provides backward compatibility to 802.11b systems Adds support for rates of 9, 18, 36, 48, and 54 Mbps

3. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 3 TGg Packet Structure: CCK-OFDM Mode Packets use existing preamble & OFDM modulation Preamble uses barker word modulation Minor modifications to 802.11b preamble OFDM Modulation used to send data Based on 802.11a Replaces PSDU of 802.11b Also adds an additional OFDM header & SIFs Pad

4. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 4 Use of.11b Header for TGg: Overview Sync Field is unchanged Used for AGC, carrier, & time acquisition Used for channel estimation (if needed) Sync Field delimiter denotes the end of the sync field Header is used convey parameters about the PSDU Indicates OFDM modulation used for PSDU Total Length of packet For CCK-OFDM, data rate is not used to determine rate Set to 2 Mbps so that all legacy equipment will decode as valid

5. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 5 Header Field for 802.11g CCK-OFDM HEADER 48 BITS Data rate is set to 2 Mbps for all OFDM rates SIGNAL 8 BITS SERVICE 8 BITS LENGTH 16 BITS CRC 16 BITS Unchanged 1 bit to denote OFDM mode. Unchanged in format. Value used is given on later slide The Length Field is adequate, since measured in usecs. OFDM proposal uses PSDU length in an integer number of usecs. 802.11 Sync Field PSDU: OFDM Modulation SFDSFD

6. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 6 b0b1b2b3b4b5b6b7 802.11b/802.11g Signal Field Data Rate Mbps = 0.1 Mbps x ( b 7 b 6 b 5 b 4 b 3 b 2 b 1 b 0 ) base 2 25.5 Mbps maximum Signal Field Definition For OFDM mode of TGg -- Data rate is not needed Maximum rate of 25.5 Mbps is inadequate The rate in the Barker modulated signal field is ignored by OFDM demodulator Data rate is contained in OFDM Signal Field For compatibility with existing network, rate is arbitrarily set at 2 Mbps See subclause 18.2.3.3 -- Data rate value is set to X’14’

7. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 7 Service Field Changes Reserved b0 Reserved b1 Locked Clock Bit 0 = not 1 = Locked b2 Mod. Selec- tion Bit 0 = CCK 1 = PBCC b3 Reserved b4 Reserved b5 Reserved b6 Length Extension Bit b7 b0b1b2b3 Reserved b4b5 Reserved b6b7 Mod. Selec- tion Bit 0 = not 1 = OFDM Locked Timing/Carrier Clocks Mandatory 802.11b Service Field New 802.11g Service Field Length Extension Bit ReservedLocked Clock Bit 0 = not 1 = Locked Mod. Selec- tion Bit 0 = CCK 1 = PBCC Reserved Identifies modulation type Not used by TGg

8. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 8 Length Field Calculation for CCK-OFDM Length(usecs) = OfdmSync + OfdmSigField + 4*Ceiling((16 + 8*LENGTH + 6 )/ N DBPS ) + SifsPad FEC Flush Bits Scrambler State & Full-Rate Service Field bits OFDMSync = 8, OfdmSigField = 4, SifsPad = 6 N DBPS : Number of data bits per OFDM Symbol Ceiling functions rounds up to nearest integer 16 bit unsigned integer -- conveys packet length useconds CCK-OFDM includes SIFS Pad & OFDM overhead Note: Length extension bit in service field is not needed

9. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 9 OFDM Preamble: Overview.11a preamble without short sync sequence Short sync purpose fulfilled by.11b preamble Long sync sequence is used for channel estimation Signal Field Conveys OFDM parameters Data rate Data Length (OFDM data length)

10. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 10 OFDM Long Sync Field Long sync follows 802.11b symbol field Defined in 802.11a, subclause 17.3.3 Referred to in 802.11a as long training symbol 2 symbols composed from 52 BPSK modulated subcarriers

11. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 11 OFDM Signal Field Signal field provides OFDM data length & rate information Defined in 802.11a, subclause 17.3.4 Conveys data rate of the OFDM data (See 17.3.4.1) Conveys length in octets of OFDM data without SIFs Pad Note: This length is not the length of the packet. Data is coded (rate =1/2) and sent using 6 Mbps mode Note that the signal field is not scrambled

12. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 12 OFDM Data Field Data Field is described in Subclause 17.3.5 Modulation depends on data rate parameter First 16 bits of data field are used as service field (17.3.5.1) First 6 bits are for scrambler initialization (all zeros) Next 10 bits are reserved (all zeros) End of data field for TGg consists of 2 parts Tail Bits -- Used for convolutional decoder flush 6 bits set to all zeros Pad Bits -- Used to fill out an OFDM symbol to proper number of bits All zeros -- number depends on data length & data rate SIFs Pad follows the data field (not the same as pad bits!)

13. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 13 SIFs Pad SIFs pad matches SIFs intervals between.11a &.11b  802.11g receivers will see a 16 usec SIFs during OFDM operation  Begin processing at end of OFDM data field  802.11b receivers will still see a 10 usec SIFs during OFDM operation  SIFs pad is cyclic extension of last data symbol

14. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 14 Transmit Frequencies Frequency range is defined in Subclause 18.4.6.1 US & Europe: 2.4 GHz to 2.4835 GHz Japan: 2.471 to 2.479 These are the same as 802.11b Channel numbering and definition in Subclause 18.4.6.2 Channel spacing is 5 MHz 14 channels identified in 18.4.6.2 Must comply with all regulatory restrictions Out-of-band emissions Power Levels

15. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 15 Transmit Spectral Mask Spectral mask is defined in Subclause 17.3.9.2. Spectral mask same as 802.11a Spectral Flatness – Subclause 17.3.9.6.2 Average energy of spectral lines +/-16 to +/-1 will deviate no more than +/-2 dB from the average Average energy for +/-26 to +/-17 will deviate no more than +2/-4 dB from the average of the +/-16 to +/-1

16. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 16 Accuracy Requirements Error Vector Magnitude specifies the transmit modulation accuracy for data Measure of MSE normalized by average power See Subclause 17.3.9.6.3 Data rate dependent Higher rates need more accuracy For TGg, EVM applies to both single carrier portion as well as the OFDM portion of the packet When the 802.11b accuracy spec is more stringent, it shall be used for the single-carrier portion Transmit center frequency tolerance: +/- 20 ppm max Symbol clock frequency tolerance: +/- 20 ppm max

17. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 17 EVM Spec from 802.11a Very high fidelity. Distortion is 25 dB down. Lower fidelity. Distortion is 5 dB down. This same fidelity is required of the 802.11g systems for 1.The single carrier portion (unless more stringent by 802.11b) 2.The OFDM portion

18. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 18 Transition Behavior To provide for the most flexibility in implementation, standard should define the waveform behavior as it transitions from single carrier to multi-carrier – Previously we only had single carrier (Barker) to single carrier (CCK) – Previously we had the same symbol rate – Standardizing the transition will allow TGg receivers to make use of the existing.11b preamble Specific areas that will be specified are: – Transmit Spectrum for Barker words – Linear transmit distortions – Power Matching between OFDM and Barker word modulation – Time alignment of the differing clocks – Termination behavior of the single carrier – Carrier Frequency and Phase

19. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 19 Transmit Spectrum for Single Carrier Key Ideas 1.Design a spectrum/time shaping pulse which makes the single- carrier portion of the signal look like OFDM. Specified pulse will meet all 802.11b requirements. 2.Make this pulse known so that the receiver can compensate the channel impulse response obtained on the single-carrier preamble for use by the OFDM portion of the packet. 3.Specify this pulse in continuous time, so that it is implementation independent. 4.For digital implementations, the pulse can be sampled at the user’s preferred implementation rate.

20. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 20 Transmit Spectrum for Single Carrier Create a single-carrier spectrum that looks like OFDM’s. It should provide a nearly flat spectrum with sufficient steep roll-off on the edges. Transmit pulse must be easily handled by 802.11b receiver. – Hence, it must have a dominate peak in the impulse response with a small amount of spread. This allows the 802.11b to lock on to this impulse response component. Want a short duration pulse to minimize implementation complexity in the transmitter Desired Characteristics

21. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 21 Transmit Pulse Design Steps 1.Choose the target spectrum. The target spectrum is a a brick wall approximation to the desired OFDM spectrum. 2.Since a brick wall spectrum has an infinite impulse response in the time domain, truncate this pulse using a continuous-time window. 3.Choose a long enough window to give the desired spectral characteristics. (Engineering judgement) 4.Choose a short enough window to minimize complexity. (Engineering judgement)

22. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 22 Target Brickwall Spectrum Limit Frequency = 27 * (20 MHz / 64 ) = 8.4375 MHz About the same as 802.11a OFDM. Associated Infinite-Duration Time Response Brickwall Spectrum

23. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 23 Truncate Impulse Response with Window Continuous Time Version Of Hanning Window Overlay of Pulse and Window

24. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 24 Impulse Response After Windowing Same duration as 802.11a Short Sync (0.8 usecs) At 22 MHz, this can be represented with an 18 tap filter Short duration provides low complexity Desired Pulse

25. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 25 Transmit Pulse for Barker Preamble Transmit Pulse shape filter defined by the following equation must be used: Digital implementations must satisfy Nyquist criterion Digital implementation must meet EVM requirement for the selected data rate Error is defined as deviation from the continuous time pulse defined above over the window

26. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 26 Linear Distortion Requirement In addition to pulse shape, there are linear distortions in the transmit and receive chain which influence the received spectrum. – For example -- SAW filter In order to re-use the channel information from the Barker preamble, these linear distortions must be the same for the barker preamble and the OFDM data.

27. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 27 Example Common Linear Distortions 802.11b Preamble/HDR Kernel OFDM Kernel SOFT SWITCH DAC Digital To Analog Converter LPF SAW Filter Low Pass Filter Up to this point the waveform Behavior is Defined by the 802.11g Standard Linear Distortions Induced On Both Signal Segments It is easy to design a transmitter to meet this requirement.

28. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 28 Requirement for Legacy Standards Barker Preamble 1 Mbps Barker Header 1 or 2 Mbps CCK 5.5 or 11 Mbps PSDU SELECTABLE @ 6, 9, 12, 18, 24, 36, 48 or 54 Mbps SIGNAL SYMBOL SSYNC 16 usecs4 usecs LSYNC 802.11b 802.11a Linear Distortions Assumed Common Linear Distortions Assumed Common This is not a new concept or requirement.

29. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 29 Requirement for 802.11g Standard Barker Preamble 1 Mbps Barker Header 1 or 2 Mbps OFDM 802.11g Linear distortions must be the same

30. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 30 Signal Power Matching Requirement 802.11b Preamble/HDR Kernel OFDM Kernel SOFT SWITCH DAC Digital To Analog Converter LPF SAW Filter Low Pass Filter Average Signal Power Must be Equal In order to maintain AGC settings, the average power seen during the Barker preamble and during the OFDM data portion must be same.

31. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 31 Transition Time Alignment The 802.11b uses a chip rate of 11 MHz. With 11 chip Barker words, the Barker words are sent at a 1 MHz rate The 802.11a OFDM uses 20 MHz sample rate. To maintain time synchronized from the Barker preambles into the OFDM data, we need to the time relationship between the end of the Barker word preamble and the beginning of the OFDM data. The 802.11b 11 MHz and 802.11a 20 MHz clocks shall be aligned on the 1 MHz boundary (e.g, each 1 useconds). The first chip of each Barker words will be centered on this 1 usec alignment. The first full 20 MHz sample of the OFDM will occur 1 usec after the zero-phase peak of 1 st chip of the last Barker word in the header. Effectively, one half-scale OFDM sample will occur before the full scale sample(for smoothing).

32. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 32 Clock Alignment on 1 usecond Alignment Epoch Alignment Epoch Every 1 usec the 802.11b Clock and 802.11a Clock Realigns

33. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 33 Transition Time Alignment Requirement 12 3 4 5 6 7 8 9 10 11 Barker Chip # 1 usec Single-Carrier: Last Barker Word Of Header Pulses Aligned On Zero-Phase Peaks Multi-Carrier: OFDM Ramp Up time 20 MHz Samples of OFDM Long Sync as described in Annex G of the 802.11a standard 11 MHz Chip Rate

34. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 34 Single-Carrier Termination Requirement When transitioning from single-carrier to multi-carrier, the single- carrier will be terminated in a controlled fashion. This termination is similar to that used for 802.11a OFDM shaping. The single-carrier signal will be terminated in nominally 100 nsecs. – Note: it is not necessary to completely flush the single-carrier pulse shaping filter. The resulting distortion to the last Barker word in the header is trivial compared to the 11 chips processing gain, thermal noise and multipath distortion. The termination can be accomplished either in the digital signal processing or by analog filtering.

35. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 35 802.11a OFDM Symbol Concatenation: Overlap and Onset/Termination This example will be used to determine the single carrier termination.

36. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 36 802.11a OFDM Symbol Onset and Termination: Mathematical Description T TR is the transition Duration.

37. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 37 Zoomed 802.11a Symbol Onset and Termination Characteristic Zoomed OFDM Symbol OnsetZoomed OFDM Symbol Termination

38. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 38 Single-Carrier Termination and OFDM Onset Requirement Single Carrier BPSK/QPSK Barker Codes Multi-Carrier OFDM time Shaped Identical to 802.11a Shaped Consistent With 802.11a ~100 nsecs

39. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 39 Transition Carrier-Frequency Requirement 802.11b Preamble/HDR Kernel OFDM Kernel SOFT SWITCH DAC Digital To Analog Converter LPF SAW Filter Low Pass Filter Carrier Frequency is coherent For both waveform segments x Local Oscillator To maintain channel information, carrier frequency must remain coherent across the single carrier to OFDM transition Receiver can maintain carrier frequency lock with PLL

40. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 40 Transition Carrier Phase Alignment Phase coherency is needed between the single- carrier and multi-carrier signal segments in order to use the channel estimate from the Barker words The receiver can exploit knowledge about the phase coherency to maintain carrier phase lock across the transition using a PLL

41. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 41 802.11b Header Modulation real imag BPSK QPSK Recall that the.11b header uses modulated Barker words Modulation is either BPSK (long preamble) or QPSK (short preamble) This will also be true for TGg systems Use the modulating phase of the last barker word to establish a phase reference for the OFDM Data

42. doc.: IEEE 802.11-01/436r0 Submission July 2001 S. Halford, et al IntersilSlide 42 Phase Reference Requirement Phase of last Barker word (not last chip!) determines the phase reference for the OFDM symbols