WWiSE Response to Written Questions

WWiSE Response to Written Questions Airgo Networks, Broadcom, Buffalo, Conexant, ETRI, Realtek, STMicroelectronics, Texas Instruments, Winbond C. Hansen, et al

WWiSE Response to Questions • Questions from Paul Feinberg (TGnSync) C. Hansen, et al

Question #1 • Did you simulate the legacy receiver performance with your proposed preamble in mixed mode? Have you simulated both auto-correlation and cross correlation types of receivers? Please provide a summary of your results for channels B, D and E. C. Hansen, et al

Answer #1 • Yes we did run simulations and measurements with existing legacy hardware to verify performance of our proposed preambles. Please clarify the 2nd part of your question. Which part of the receiving process are you referring to? C. Hansen, et al

Question #2 • We understand that PER=10^-2 with SNR=3dB is worst case, i.e., in channel-D, for 6.75Mbps. We also understand that the data portion would be transmitted using STBC for this data rate. But SIG-N (and SIG-MM in mixed mode) doesn’t utilize STBC. Does this mean that the bit error at SIG-N would be dominant for a PER in these lower SNR regions. Do these results include the impact of errors in SIG-N (and SIG-MM)? Please provide error rate curves. • * What is the impact of using QPSK and SIG-N at such a low SNR? • * The disclosed simulated results for CC59 and CC67 do not indicate whether they are for mixed mode and/or green field mode. Please clarify. C. Hansen, et al

Answer #2 • The effect of the error rate on the signal field relative to the entire frame will depend on the frame length. For long frames, the frame error rate will be dominated by bit errors in the data, not the signal field. • The disclosed simulation results were for green field mode. C. Hansen, et al

Question #3 • Frequency offset estimation and timing offset estimation at low SNR region, such as SNR=3dB, would be more difficult with 2 pilot tones in 20MHz than with 4 pilots. Do you need advance receiver techniques to get acceptable performance? Would you show us the performance degradation of reduced pilot tones to compare with 4 pilot tones in 20MHz? C. Hansen, et al

Answer #3 • Our pilot technique is designed to be robust and efficient in a wide range of channels. No advanced receiver techniques are necessary. There is less than 0.1 dB performance degradation compared to the legacy 4 pilot scheme on channel models B and D. C. Hansen, et al

Question #4 • With 3 or more transmit antennas, your proposal does not provide STBC for the transmission of one spatial stream. How do you propose to transmit one spatial stream when you have more than 2 transmit antennas? C. Hansen, et al

Answer #4 • The WWiSE proposal does not define a specific mode for transmitting one spatial stream with more than two antennas. With one transmit stream, more than two transmit antennas provides a diminishing benefit. C. Hansen, et al

Question #5 • What is the accuracy of your power measurements in the short sequence relative to the power of the data portion of the PPDU? Please provide performance results. C. Hansen, et al

Answer #5 • Our simulation results indicate that the power difference between the short training sequence and the data sequence is small – less than 0.5 dB rms. C. Hansen, et al

Question #6 • The proposed LS field is efficiently shortened but it is a tradeoff between the efficiency and the receiver complexity. In terms of the channel estimation, additional complexity to separate spatial streams would be required. Do you control the IP that is used for your channel estimation scheme? Will you disclose your algorithms? • (Especially, in 3 or 4 Tx-antennas case, it seems that very accurate frequency offset compensation would be required for addition and subtraction among two LSs.) C. Hansen, et al

Answer #6 • Channel estimation has been thoroughly investigated in the open literature for many years. We believe these algorithms are applicable to our proposal and every other 802.11n proposal. • For further information on our IP position, please see our web site, www.wwise.org C. Hansen, et al

Question #7 • How will you address the interaction between mixed mode, GF and legacy BSS mode? In such cases, a frame might be received by an unexpected node in another BSS. . How will the receiver operate in the cases listed below? • 　 legacy Tx ----> MM Rx : ? • MM Tx ----> legacy Rx : ? • legacy Tx ----> GF Rx : ? • GF Tx ----> legacy Rx : ? • MM Tx ----> GF Rx : ? • GF Tx ----> MM Rx : ? C. Hansen, et al

Answer #7 • Please clarify the meaning of an “unexpected node”. • The WWiSE proposal contains mechanisms for working with 802.11b, 802.11g, and 802.11a legacy equipment. C. Hansen, et al

Question #8 • Given that the Alamouti STBC patent is so broadly defined, is it possible to implement the WWiSE proposal without utilizing the Alamouti STBC patent? C. Hansen, et al

Answer #8 • All STBC modes in the WWiSE proposal are optional. See 11-04/886r5. C. Hansen, et al

Question #9 • What is the reason for performing MSDU aggregation before sequence number assignment? • Without sequencing and FCS for individual MSDU, you cannot facilitate individual MSDU retransmission. There are some losses in MAC throughput efficiency. Please justify. C. Hansen, et al

Answer #9 • MSDU aggregation is much simpler to implement than MPDU aggregation. Under low error conditions MSDU aggregation is more efficient than MPDU aggregation. In high error environments the effectiveness of MPDU aggregation is unclear. The WWiSE proposal, with the HTP burst mechanism combined with MSDU aggregation, offers greater flexibility for these environments. C. Hansen, et al

Question #10 • Can your HTP Bursting and A-PPDU be applied to multiple receivers? If so, how can the receivers schedule the response? Is the multi-receiver HTP Bursting and A-PPDU sent with no-ACK policy or Delayed BlockACK policy? C. Hansen, et al

Answer #10 • Yes, HTP burst and A-PPDU can be applied to multiple receivers. All variants of the ACK mechanism are possible. In our simulations we employed no-ACK and Delayed Block ACK as appropriate with excellent throughput while meeting all QoS goals. C. Hansen, et al

Question #11 • How does the MAC distinguish between the use of ZIFS and A-PPDU for multiple receiver aggregation? C. Hansen, et al

Answer #11 • A-PPDU transmissions are indicated by the LPI bit in the TXVECTOR. C. Hansen, et al

Question #12 • What is the reason to restrict MSDU aggregation per priority instead of per AC or TSID? C. Hansen, et al

Answer #12 • The aggregation defined in the WWiSE proposal is performed above the security mechanisms. C. Hansen, et al

WWiSE Response to Questions • Questions from Joseph Levy (Interdigital) C. Hansen, et al

Question #13 • Have you used soft or hard symbol Viterbi decoder? • Regarding document: 11-04-0877-04-000n-wwise-proposal-response-to-frcc.doc C. Hansen, et al

Answer #13 • A soft decoder was used in the simulations for 11-04-0877-04. C. Hansen, et al

Question #14 • Can you please justify your assumption that all STAs in the service area can be supported at a data rate of 135 Mbps as assumed in the MAC simulations? To what do you attribute your PHY performance advantage relative to TGnSync? (The TGnSync average data rate is lower and some STA in the service area have even lower data rates.) C. Hansen, et al

Answer #14 • This was an editorial error in the indicated PHY rates for one table in this document. The actual PHY rates were lower for some STAs. A corrected version has been uploaded to the server. C. Hansen, et al

Question #15 • What is your frame size in your simulation curve figure 2 (Section 4.3.2)? C. Hansen, et al

Answer #15 • These were 1000 bytes frames. C. Hansen, et al

WWiSE Response to Questions • Questions from Pratik Mehta (Dell) C. Hansen, et al

Question #16 • Backwards Compatibility: Please clarify your proposal to address backwards-compatibility with 11a, b, g. For example, I have heard generic statements about backwards-compatibility with 11a and 11g, but more detail is requested. Also, the compatibility with 11b has not been very clear, and therefore specific treatment of this aspect is requested. C. Hansen, et al

Answer #16 • The WWiSE proposal includes mixed mode frame formats for PHY level backward compatibility with 802.11a and 802.11g. Furthermore, the WWiSE proposal supports the MAC level protection mechanisms of 802.11g for backward compatibility with 802.11b. C. Hansen, et al

Question #17 • Heterogeneous Clients in a network: When 11g was introduced, there were questions about what a mixed set of clients would yield in terms of performance. There was much confusion and lack of good information around this. How does your proposal in TGn address this, and what expectations can you set about mixed networks? C. Hansen, et al

Answer #17 • This topic is addressed in our response to Comparison Criterias 15, which can be found in section 5.1 of 11-4-877r4. C. Hansen, et al

Question #18 • Mandatory/Optional Aspects: What aspects of your proposal are mandatory or optional? Which ones of the optional features do you believe apply to one or more broad-based markets? Are there any features in your proposal which include more than one way of providing for, and if so could you please describe those? C. Hansen, et al

Answer #18 • The 2 transmit antenna (2 transmit stream), 20 MHz bandwidth, convolutional coded modes are mandatory. All other modes are optional. C. Hansen, et al

Question #19 • How scaleable is your proposal over time to increase performance, decrease power consumption, QoS, Security, Management, etc? How will your proposal address such needs of the future without having to develop yet another standard/amendment very quickly after TGn. C. Hansen, et al

Answer #19 • Our proposal scales with both bandwidth (to 40 MHz) and number of transmit antennas (to 4) to increase performance. Our proposal is compatible with 802.11e and 802.11i. C. Hansen, et al

WWiSE Response to Written Questions