doc.: IEEE / 0710r1 Submission May 2015 Gigaray Communication Variable Length Guard Interval for 45GHz Date: Authors: NameAffiliationsAddressPhone Feng Huang Gigaray Communication Wuxi Yan Li Gigaray Communication Wuxi Haiming Wang Southeast University (SEU) Nanjing Shiwen He Southeast University (SEU) Nanjing Slide 1

doc.: IEEE / 0710r1 Submission May 2015 Gigaray Communication SC-Modulation and OFDM-Modulation Single carrier (SC) modulation has low PAPR and higher transmitting power efficiency, but requires complicated equalization to combat multipath. OFDM modulation offers good performance in multipath environment with simple frequency domain equalization, but suffers from high PAPR and relatively lower transmitting power efficiency. Both single carrier modulation and OFDM modulation are adopted by millimeter wave (mmw) WLAN to balance the advantage and shortcoming of two modulation schemes. Slide 2

doc.: IEEE / 0710r1 Submission May 2015 Gigaray Communication Equalization for SC-modulation and OFDM modulation Traditionally, time-domain equalization (TD-EQ) using complex adaptive filters is used for single carrier system. For mmw communication system, high symbol rate means long adaptive filters even if the channel delay spread is short. When inter-carrier-interference is not severe, simple one- tap frequency-domain equalization (FD-EQ) is sufficient for OFDM system. It is expensive to support both time-domain and frequency- domain equalization and, in general, it desirable to use FD- EQ for both SC and OFDM modulation. Slide 3

doc.: IEEE / 0710r1 Submission May 2015 Gigaray Communication Signal structure to enable FD-EQ OFDM uses cyclic prefix (CP, also referred as guard interval, GI) to avoid inter-symbol-interference introduce by multipath channel, also maintain frequency orthogonal. OFDM signal structure To enable FD-EQ for SC modulation, similar structure is adopted Slide 4

doc.: IEEE / 0710r1 Submission May 2015 Gigaray Communication Transmitter latency of CP processing Traditional SC transmitter without CP sends data symbol out immediately once it is generated. SC transmitter with CP has to buffer data symbols to enable the insertion of CP. This introduces latency and increases the complexity of transmitter. Slide 5

doc.: IEEE / 0710r1 Submission May 2015 Gigaray Communication Pseudo-random sequence GI for SC modulation Propose using pseudo-random sequence as guard interval for SC modulation The K-length pre-sequence before the M SC symbols can be treated as CP to the K-length post-sequence. M+K=N and N=2 m, N point FFT can be used for FD-EQ Pseudo-random sequence is zero correlation zone (ZCZ) sequence [1]. Chip-level π/2-QPSK modulation for pseudo-random sequence Slide 6

doc.: IEEE / 0710r1 Submission May 2015 Gigaray Communication Benefits of Pseudo-random Sequence GI Reduced transmitter data processing latency and complexity Receiver performance improvement [1] by utilizing known pseudo-random sequence for more frequent updates of –FFT trigger point tracking –channel estimation tracking –sampling timing offset tracking –carrier offset tracking Slide 7

doc.: IEEE / 0710r1 Submission May 2015 Gigaray Communication Variable Guard Interval Length Delay spread can change dramatically in indoor environment. For mmw communication, the delay spread is relative large during the registration to an AP and initial training stages. After the beam forming is activated, the delay spread usually become smaller. Have variable guard interval length can balance the communication performance and efficiency. Slide 8

doc.: IEEE / 0710r1 Submission May 2015 Gigaray Communication Proposed Guard Interval Lengths Two guard interval options SC modulation –256-symbol scenario 64 ZCZ sequence and 192 data symbols to form a sub-block 32 ZCZ sequence and 224 data symbols to form a sub-block –512-symbol scenario 128 ZCZ sequence and 384 data symbols to form a sub-block 64 ZCZ sequence and 448 data symbols to form a sub-block OFDM modulation –1/4 and 1/8 CP 1-bit signaling field to indicate the guard interval length Slide 9

doc.: IEEE / 0710r1 Submission May 2015 Gigaray Communication ZCZ Sequences (1) The ZCZ sequence is designed by the iteration with Discrete Fourier Transform (DFT) matrix and cofficient matrix, based on initial mutually orthogonal aperiodic sequence sets [1]. The chip of ZCZ seuqences is composed by four phase {+1, +j, - 1, -j} 。 The four phases are represented by 0, 1, 2, and 3 in the following sequence definition. The ZCZ sequence of length 32 is The maximal normalized periodic auto-correlation side lobe peak is Slide 10

doc.: IEEE / 0710r1 Submission May 2015 Gigaray Communication ZCZ Sequences (2) The ZCZ sequence of length 64 is The maximal normalized periodic auto-correlation side lobe peak is 0.25 The ZCZ sequence of length 128 is The maximal normalized periodic auto-correlation side lobe peak is Slide 11

doc.: IEEE / 0710r1 Submission May 2015 Gigaray Communication Data field structure Slide 12

doc.: IEEE / 0710r1 Submission May 2015 Gigaray Communication Conclusion Propose ZCZ sequence for guard interval of single carrier modulation for lower transmitter latency and improved receiver performance Propose two guard interval length to adapt to delay spread variations Propose 1-bit signaling field to indicate guard interval length Slide 13

doc.: IEEE / 0710r1 Submission May 2015 Gigaray Communication References [1]. Preamble Sequence for aj (45GHz) ( aj). Proposal of IEEE802.11aj(45GHz). Slide 14