doc.: IEEE 802.11-15/ 710r0

Submission

May 2015

Variable Length Guard Interval for 45GHz

Date: 2015-05-19

Authors:

Name Affiliations Address Phone Email

Feng HuangGigaray Communication

Wuxi China feng_huang@gigaray.cn

Yan LiGigaray Communication

Wuxi China yan_li@gigaray.cn

Haiming WangSoutheast University (SEU)

Nanjing China hmwang@seu.edu.cn

Shiwen HeSoutheast University (SEU)

Nanjing China hesw01@seu.edu.cn

Slide 1

doc.: IEEE 802.11-15/ 710r0

Submission

May 2015

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.

doc.: IEEE 802.11-15/ 710r0

Submission

May 2015

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.

doc.: IEEE 802.11-15/ 710r0

Submission

May 2015

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

doc.: IEEE 802.11-15/ 710r0

Submission

May 2015

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.

doc.: IEEE 802.11-15/ 710r0

Submission

May 2015

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=2m, N point FFT can be used for FD-EQ• Pseudo-random sequence is zero correlation zone (ZCZ)

sequence. • Chip-level π/2-QPSK modulation for pseudo-random

sequence

doc.: IEEE 802.11-15/ 710r0

Submission

May 2015

Benefits of Pseudo-random Sequence GI

• Reduced transmitter data processing latency and complexity

• Receiver performance improvement 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

doc.: IEEE 802.11-15/ 710r0

Submission

May 2015

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.

doc.: IEEE 802.11-15/ 710r0

Submission

May 2015

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

doc.: IEEE 802.11-15/ 710r0

Submission

May 2015

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.

• 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 - 22110220222220132233020222002031- The maximal normalized periodic auto-correlation side lobe

peak is 0.3536

doc.: IEEE 802.11-15/ 710r0

Submission

May 2015

ZCZ Sequences (2)

• The ZCZ sequence of length 64 is- 21010002230313112101111301210200210122202303

31332101333101212022- The maximal normalized periodic auto-correlation side

lobe peak is 0.25• The ZCZ sequence of length 128 is

- 00112020222220132211022000220213001120201111130200332002113313200011202000000231221102202200203100112020333331200033200233113102

- The maximal normalized periodic auto-correlation side lobe peak is 0.3536

doc.: IEEE 802.11-15/ 710r0

Submission

May 2015

Data field structure

doc.: IEEE 802.11-15/ 710r0

Submission

May 2015

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