doc.: ieee 802.11-15/ 0710r1 submission may 2015 gigaray communication variable length guard...
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doc.: IEEE 802.11-15/ 0710r1
Submission
May 2015
Gigaray Communication
Variable Length Guard Interval for 45GHz
Date: 2015-05-19
Authors:
Name Affiliations Address Phone Email
Feng HuangGigaray Communication
Wuxi China [email protected]
Yan LiGigaray Communication
Wuxi China [email protected]
Haiming WangSoutheast University (SEU)
Nanjing China [email protected]
Shiwen HeSoutheast University (SEU)
Nanjing China [email protected]
Slide 1
doc.: IEEE 802.11-15/ 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 802.11-15/ 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 802.11-15/ 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 802.11-15/ 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 802.11-15/ 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=2m, 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 802.11-15/ 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 802.11-15/ 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 802.11-15/ 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 802.11-15/ 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
- 22110220222220132233020222002031
- The maximal normalized periodic auto-correlation side lobe peak is 0.3536
Slide 10
doc.: IEEE 802.11-15/ 0710r1
Submission
May 2015
Gigaray Communication
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
Slide 11
doc.: IEEE 802.11-15/ 0710r1
Submission
May 2015
Gigaray Communication
Data field structure
Slide 12
doc.: IEEE 802.11-15/ 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 802.11-15/ 0710r1
Submission
May 2015
Gigaray Communication
References
[1]. Preamble Sequence for 802.11aj (45GHz) (11-14-1398-01-00aj). Proposal of IEEE802.11aj(45GHz).
Slide 14