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Co-time Co-frequency Full Duplex for 802.11 WLAN

Co-time Co-frequency Full Duplex for 802.11 WLAN. Date: 20 13-07-15. Authors:. Abstract. HEW aims at improving the transmission efficiency of WLAN.

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Co-time Co-frequency Full Duplex for 802.11 WLAN

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  1. Co-time Co-frequency Full Duplex for 802.11 WLAN Date: 2013-07-15 Authors: Hongliang Bian (China Telecom)

  2. Abstract HEW aims at improving the transmission efficiency of WLAN. This presentation briefly introduces a new PHY technology called Co-time Co-frequency Full Duplex (CCFD) transmission. It intends to share the latest research study information and to facilitate further investigation and discussion on full-duplex transmission technology on WLAN. Hongliang Bian (China Telecom)

  3. Background (1/2) • WLAN has been widely used in indoor and outdoor environment to provide • home wireless networking, • enterprise and campus wireless networks, • cellular offload hotspot networks. • Next generation WLAN network needs to accommodate more users and provide higher regional data throughput. • WLAN operates on license exempt spectrum, and frequency bands are limited. Therefore it may be necessary to consider some new technologies to further improve spectrum efficiency. Hongliang Bian (China Telecom)

  4. Background (2/2) • Wireless Communication Mechanisms Include Functions • Multiple access to the shared medium. • Duplex transmission over the same medium for the pair communicating stations • Duplex Transmission Mechanisms Include • Half duplex transmission. In the half duplex transmission, both communicating stations cannot transmit information at same time, such as walky-talky. • Full duplex transmission, on the other hand, allows both communicating stations to exchange information simultaneously over the same medium. • In order to support full duplex communication over half-duplex link, wireless transmission operates on • Frequency division duplexing (FDD) • Time division duplexing (TDD) Hongliang Bian (China Telecom)

  5. Co-time Co-frequency Full Duplex (CCFD) (1/2) • Current 802.11 technologies only use TDD scheme and allows transmission and reception at different time, causing low medium usage efficiency. • CCFD allows transmission and reception simultaneously over the same frequency, which could improve the spectrum efficiency significantly. STA1 (bits/s/Hz) full-duplex limit full-duplex half-duplex STA 1 STA2 (bits/s/Hz) STA 2 Hongliang Bian (China Telecom)

  6. Co-time Co-frequency Full Duplex (CCFD) (2/2) STA 1 STA 2 Key challenge: Self-interference from the transmitter of one station to its own receiver and interference from the transmitter of stations other than the target station is the key issue. Interference cancellation is critical to the full-duplex transmission. Hongliang Bian (China Telecom)

  7. Interference Cancellation There are a quite few full-duplex transmission academic study reports. Current those studies mainly focus on self-interference cancellation specific to the point to point communication. Three types of self-interference cancellation schemes: • Antenna cancellation • Analog cancellation • Digital cancellation Hongliang Bian (China Telecom)

  8. Antenna Cancellation (1/2) • Asymmetric Antenna Placement • Distance difference from two transmit antennas to receive antenna is an odd number of λ/2, which provides an inverse phase difference between the two self interferences. • Factors that influence antenna cancellation performance: • Placement accuracy of transmit antennas • Power balance of self interferences • Signal bandwidth Distance mismatch effect on antenna cancellation[1] Amplitude mismatch effect on antenna cancellation[1] Hongliang Bian (China Telecom)

  9. Antenna Cancellation (2/2) • Symmetric Antenna Placement • Benefits of symmetric placement compared to asymmetric placement: • Receive cancellation and transmit cancellation can be combined with placement of both symmetric Rx antennas and symmetric Tx antennas. • Symmetric antenna placement can be extended to support MIMO easily. With a π phase inversion between two symmetric Rx/Tx antennas, self interference can be cancelled at Tx/Rx antenna. The main factor needs to be considered is distance mismatch of the pair of Rx/Tx antennas. Double antenna cancellation with receiving cancellation plus transmitting cancellation[2] Hongliang Bian (China Telecom)

  10. Analogy Cancellation • Take the known interference and received signals as input and outputs the received signal with the suppressed self interference. • Noise cancellation ASIC can be used to adjust the amplitude and phase of the interference reference signal to match the self interference.[3] • Factors that influence analogy cancellation performance: • Accuracy of adjustment of the amplitude and phase of the interference reference signal is key issue. • Adaptive adjustment of the interference reference signal according to the output signal may need to be considered. Hongliang Bian (China Telecom)

  11. Digital Cancellation • Given that the input signal from the RF receiver module doesn't saturate the ADC, the digital cancellation can be performed to further remove the residual of self-interference from the transmitter. Digital interference reference signal is derived from transmitting signal, then it is subtracted in the output of the baseband so that the self interference can be removed. • Factors that influence digital cancellation performance: • ADC dynamic range • SINR of the output of ADC • Quantification method ADC DAC - TX PHY Digital feedback RX PHY TX MAC RX MAC Hongliang Bian (China Telecom)

  12. Summary • Full-duplex creates a new promising for improving medium efficiency. But some challenges in the full-duplex transmission need further investigation before the technology becomes feasible in the real world. • Performance of antenna cancellation is very sensitive to the AP placement. It needs to improve the self-interference cancellation performance of individual AP which can’t be managed professionally. • Multi-path signal will degrade the performance of self-interference cancellation, especially for indoor scenario. • Digital cancellation performance is limited by the dynamic range and quantification method of ADC. For some amplitude sensitive modulation/demodulation schemes such as OFDM, it needs higher dynamic range and specific quantification method of ADC. • Since the analog cancellation and digital cancellation can be performed together, it may need to coordinate the analog cancellation and digital cancellation to improve and optimize the performance. Hongliang Bian (China Telecom)

  13. Conclusion This presentation proposes a Co-time Co-frequency Full Duplex technology for improving the spectrum efficiency. • Proposal 1: The full-duplex transmission needs to be considered in HEW. • Proposed 2: Self interference cancellation performance and algorithms for full-duplexer should be further studied. • Proposal 3: Impacts to the current WLAN should be investigated and backward compatibility to legacy WLAN needs to be careful considered. Hongliang Bian (China Telecom)

  14. References • [1] Choi J I, Jain M, Srinivasan K, et al.. Achieving single channel, full duplex wireless communication [C]. Proceedings of the 16th Annual International Conference on Mobile Computing and Networking (MobiCom '10), New York, 2010: 1–12. • [2] Khojastepour M A, Sundaresan K, Rangarajan S, et al.. The case for antenna cancellation for scalable full-duplex wireless communications [C]. 10th ACM Workshop on Hot Topics in Networks (HOTNETS '11), Massachusetts, USA, 2011: 17-17. • [3] Jain M, Choi J I, Kim T M, et al.. Practical, real-time, full duplex wireless [C]. Proceedings of the 17th Annual International Conference on Mobile Computing and Networking (MobiCom '11), New York, 2011: 301-312. Hongliang Bian (China Telecom)

  15. Thank You! Hongliang Bian (China Telecom)

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