Foundations for Hierarchical Full-duplex Networks

NSF NeTS Large

List of personnel

  1. Principal Investigator (OSU): Ness Shroff

  2. Principal Investigators (Rice): Ashutosh Sabharwal, Edward Knightly, and Lin Zhong

  3. Principal Investigator (UCLA): Suhas Diggavi

  4. Postdoctoral Scholar: Changhee Joo

  5. Graduate Students: Zhenzhi Qian, Fei Wu, and Yang Yang

Project goals

In the overall project, our overarching goal is to develop foundational principles for hierarchical wireless network design by leveraging full-duplex transmissions in both access and wireless backhaul. Full-duplex is most promising at shorter ranges, and hence is fortuitously aligned with the predicted dominant access range in future networks. Furthermore, larger full-duplex ranges are feasible in infrastructure-to-infrastructure links, and hence are well suited for backhaul links. While full-duplex is well-aligned with the key elements of hierarchical networks, our current design principles are largely developed for half-duplex transmissions which is the basis for all current networks. The project goals are to develop data-driven signal models for full-duplex to facilitate information-theoretic analyses and foundations for network-scale resource allocation.

Overall project website:

Major Activities:

  1. Low-complexity scheduling mechanism for full duplex communication with “cut through routing:" The recent breakthrough in wireless full-duplex communication makes possible a brand new way of multi-hop wireless communication, namely full-duplex cut-through transmission, where for a traffic flow that traverses through multiple links, every node along the route can receive a new packet and simultaneously forward the previously received packet. This wireless transmission scheme brings new challenges in the design of MAC layer algorithms that aim to reap its full benefit. Shroff et. al have developed a new way to characterize the interference relationship between links in the network with cut-through transmission which decouples the routing decision with the scheduling decision and enables a seamless adaptation of traditional half-duplex routing/scheduling algorithm into wireless networks with full-duplex cut-through capabilities. Based on this interference model, a queue-length based CSMA-type scheduling algorithm is proposed, which both leverages the flexibility of full-duplex cut-through transmission and permits distributed implementation. This work has been published in IEEE INFOCOM 2015.

  2. Low-Feedback Wireless multicast: For a multicast group of n receivers, existing techniques either achieve high throughput at the cost of prohibitively large (e.g., O(n)) feedback overhead, or achieve low feedback overhead but without either optimal or near-optimal throughput guarantees. Simultaneously achieving good throughput guarantees and low feedback overhead has been an open problem and could be the key reason why wireless multicast has not been successfully deployed in practice. In recent work, Shroff et. al have developed a novel anonymous-query based rate control, which approaches the optimal throughput with a constant feedback overhead independent of the number of receivers. In addition to our theoretical results, through implementation on a software-defined ratio platform, we show that the anonymous-query based algorithm achieves low-overhead and robustness in practice. This work will appear in ACM Mobihoc 2016.

  3. Impact of Limited Channel State Information on Massive MIMO Network Performance: In recent years, there have been significant efforts on the research and development of Massive MIMO (M-MIMO) technologies at the physical layer. So far, however, the understanding of how M-MIMO could affect the performance of network control and optimization algorithms remains rather limited. In this work, Shroff et. al have focused on analyzing the performance of the queue-length-based joint congestion control and scheduling framework (QCS) over M-MIMO cellular networks with limited channel state information (CSI). Our contributions in this paper are two-fold: i) We characterize the scaling performance of the queue-lengths and show that there exists a phase transitioning phenomenon in the stead-state queue-length deviation respect to the CSI quality (re- flected in the number of bits B that represent CSI); and ii) We characterize the congestion control rate scaling performance and show that there also exists a phase transitioning phenomenon in steady-state congestion control rate deviation respect to the CSI quality. Collectively, the findings in this paper advance our understanding of the trade-offs between delay, throughput, and the accuracy/complexity of CSI acquisition in M-MIMO cellular network systems. This work will appear in ACM Mobihoc 2016. In related work, Bai and Sabharwal have considered using unlicensed bands as side channels to aid the instantaneous cancellation of inter-node interference. The side channels allow direct communication between the uplink transmitters and the downlink receivers, through which the downlink receivers can gain some information on the inter-node interference and then alleviate the effect of it. The focus of that work has been on characterizing the information-theoretic capacity of the side-channel assisted system under fixed channel gains without taking the channel-level and packet-level dynamics into consideration. The key problem we are targeting is to design scheduling algorithms that make the following three decisions (a) which uplink and downlink users to be activated simultaneously; (b) how to assign side-channel to different uplink transmitters; (c) which packet to be transmitted on the main channel and which packet to be transmitted on the side channel, while taking into account the packet-level and channel-level dynamics, with an aim to support the maximum possible downlink/uplink packet arrival rates. This work is being jointly conducted by PIs Shroff (OSU) and Sabharwal (Rice).

  4. Characterizing the gains that can be achieved in wireless networks with a fixed number of RF chains: The motivation for fixing the RF chains is to compare the performance of full duplex with various techniques that can exploit multiple RF chains. Shroff et. al have characterized both theoretically and experimentally, where the proof of concept is demonstrated by actual implementation. Part of this work has appeared in IEEE INFOCOM 2014.

  5. Scheduling for multi-antenna systems with full duplex capability: In ongoing work between Shroff (OSU) and Sabharwal (Rice) we have focused on scheduling for multi-antenna systems with full duplex capability. Even some simple suboptimal schemes such as zero-forcing beam-forming or conjugate beam-forming require the instantaneous channel state information, which is hard to obtain in practice. To make things worse, the scheduling algorithm using these dynamic beam-forming schemes need to have the complete channel state information for all the users in order to find the best M users to serve. Hence, we propose to develop simple scheduling algorithms that rely on limited feedback for this system.

  6. Scheduling algorithms with decisions on side-channel information: In collaborative work between Sabharwal (Rice) and Shroff (OSU) we have we have designed scheduling algorithms that decides when the uplink, downlink, side-channels should be turned on, and which packets to be transmitted on these three links, based on the instantaneous channel knowledge and the queue backlog information. We have focused on a single cell network with half-duplex users and a full-duplex base-station. The full-duplex capability at the base-stations permits simultaneous uplink and downlink transmissions over the same band and thus can bring up to two-fold gain in cell throughput. However, the full-duplex transmission mode leads to an inter-node interference which can significantly reduce the downlink transmission rate and result in only marginal gain compared with the half-duplex mode, especially when there are more than 1 activated uplink transmitter. The proposed algorithm is proven to be near throughput-optimal.

Broader Impacts:

The research results have been published in peer-reviewed journals and conferences. The PIs have given several talks at various universities and companies that have highlighted the key contributions of the project. PI Shroff arranged and moderated a panel on full duplex communications at Mobihoc 2014 (where PI Sabharwal was also a panelist) and also gave a series of lectures 2014 Lipari School on "Network Analysis, Design and Optimization”, in July in Italy, where a part of the research outcomes in this project were discussed.

PI Shroff was also general chair of WiOPT 2016, where research on multi-antenna technologies and full duplex were actively discussed.

PostDoc John Tadrous has attended multiple invited symposiums and workshops during this reporting period. First, he was invited to the NSF NeTS Early Career workshop in July, 2015, where he presented research conducted as part of this project. Secondly, he was invited to present as part of Intel Corporation’s 5G Workshop on September 24-25th. Finally, he disseminated research results at the 14th International Symposium on Modeling and Optimization in Mobile, Ad Hoc and Wireless Networks (WiOpt 2016) in May, 2016.

Graduate Student Xu Du and PostDoc Tadrous attended the 16th IEEE International Workshop on Signal Processing Advances in Wireless Communications (SPAWC 2015), held in Stockholm, Sweden, where they presented on “MU-MIMO Beamforming with Full-duplex Open-loop Training”.

Graduate Students Andrew Kwong and Xing Zhang attended the 2015 Conference on Signals, Systems, and Computers (Asilomar), where they presented “Overcoming Conjugate Beamforming Limitations with Side-Channel Cooperative Decoders” and “Angle of arrival based beamforming schemes for massive MIMO FDD systems”.

PI Sabharwal attended the Radio Frequency Integrated Circuits (RFIC) conference in Tampa, FL, to present his paper “Design Tradeoff in Full-duplex Wireless”.

Post-doc Tadrous and graduate student Xu attended the 2014 Asilomar Conference on Signals, Systems, and Computers in November 2014, to present their paper “MIMO broadcast channel with continuous feedback using full-duplex radios”.

Graduate student Evan Everett attended the IEEE International Symposium on Information Theory in Honolulu, HI, to present his research “A signal-space analysis of spatial self-interference isolation for full-duplex wireless”.

Co-PI Knightly presented a keynote, WiFi in sub-GHz Bands: Research Advances and Global Trials, at IEEE LatinCom, Cartagena, Colombia, November 2014.


  1. J. Bai, C. Dick, and A. Sabharwal, "Vector Bin-and-cancel for MIMO Distributed Full-duplex", submitted to IEEE Transactions on Information Theory, 2014.

  2. J. Bai, C. Liu, and A. Sabharwal, "Increasing cellular capacity using ISM band side-channels: a first study", in Proc. of the 4th workshop on All things cellular: operations, applications, & challenges (AllThingsCellular '14). ACM, New York, NY, USA, 9-14. DOI=10.1145/2627585.2627586.

  3. "On the degrees-of-freedom of multi-user MIMO full-duplex network", to be presented to IEEE ISIT 2015, Hong Kong.

  4. E. Everett, A. Sabharwal, "A Signal-Space Analysis of Spatial Self-Interference Isolation for Full-Duplex Wireless", IEEE ISIT 2014. Honolulu, HI.

  5. H. Yu, O. Bejarano, and L. Zhong, "Combating Inter-cell Interference in 802.11ac-based Multi-user MIMO Networks", in Proc. of ACM MobiCom 2014, Maui, Hawaii.

  6. S. Mishra, I-H. Wang, and S. Diggavi, "Harnessing Bursty Interference in Multicarrier Systems with Feedback", IEEE ISIT 2014, Honolulu, HI.

  7. J. Hachem, N. Karamchandani, and S. Diggavi, "Multi-level Coded Caching", IEEE ISIT 2014, Honolulu, HI.

  8. A. Sabharwal, P. Schniter, D. Guo, D. Bliss, S. Rangarajan, and R. Wichman, "In-band Full-duplex Wireless: Challenges and Opportunities", IEEE JSAC Special Issue on Full-duplex Wireless Communications and Networking.

  9. A. Flores and E. Knightly, "Virtual Duplex: Scaling Dense WLANs and Eliminating Contention Asymmetry", in Proc. of IEEE Workshop on Cognitive Radio Architectures for Broadband, Raleigh, NC, October 2014.

  10. X. Zhang, J. Tadrous, F. Xue, E. Everett, and A. Sabharwal, "Angle of arrival based beamforming schemes for massive MIMO FDD systems", submitted, IEEE Asilomar Conference on Signals, Systems and Computers (ASILOMAR), Nov. 2015.

  11. X. Du, J. Tadrous, C. Dick, and A. Sabharwal, "MU-MIMO beamforming with full-duplex open-loop training", to appear, The 16th IEEE International Workshop on Signal Processing Advances in Wireless Communications, SPAWC 2015, July 2015.

  12. X. Du, J. Tadrous, C. Dick, and A. Sabharwal, "MIMO broadcast channel with continuous feedback using full-duplex radios", IEEE Asilomar Conference on Signals, Systems and Computers (ASILOMAR), vol., no., pp.1701,1705, 2-5 Nov. 2014.

  13. A. Kwong and A. Sabharwal, "Overcoming Conjugate Beamforming Limitations with Side-Channel Cooperative Decoders", submitted to Asilomar Conference on Signals, Systems and Computers, May 2015.

  14. E. Everett, and A. Sabharwal, "Spatial Self-Interference Isolation for In-Band Full-Duplex Wireless: A Degrees-of-Freedom Analysis", submitted to IEEE Transactions on Information Theory, 2014.

  15. F. Wu, Y. Sun, Y. Yang, K. Srinivasan, and N. B. Shroff, "Constant Delay and Constant Feedback Moving Window Network Coding for Wireless Multicast: Design and Asymptotic Analysis", in IEEE Journal on Selected Areas in Communications, vol. 33, no. 2, Mar. 2015, pp. 127 – 140.

  16. Y. Yang and N. B. Shroff, "Scheduling in Wireless Networks with Full-Duplex Cut-through Transmission", IEEE INFOCOM'15, Hong Kong, April 2015.

  17. Y. Yang, B. Chen, K. Srinivasan, N. B. Shroff, "Characterizing the Achievable Throughput in Wireless Networks with Two Active RF chains", in Proceedings of the IEEE INFOCOM’14, Toronto, Canada, April 2014.

  18. Z. Qian, B. Ji, K. Srinivasan, and N. B. Shroff, "Achieving Delay Rate-function Optimality in OFDM Downlink with Time-correlated Channels", IEEE INFOCOM'16, San Francisco, CA, Apr. 2016.

  19. S. Misra, X. Lin, and N. B. Shroff, "Fast Multi-Channel Gibbs-Sampling for Clustering in Cloud-Based Radio Access Networks", IEEE WiOpt'16, Tempe, AZ, May, 2016.

  20. C. Joo, X. Lin, J. Ryu, and N. B. Shroff, "Distributed Greedy Approximation to Maximum Weighted Independent Set for Scheduling with Fading Channels", IEEE/ACM Trans. on Networking (ToN), accepted for publication.

  21. F. Wu, Y. Yang, O. Zhang, K. Srinivasan, and N. B. Shroff, "Anonymous-Query based Rate Control for Wireless Multicast: Approaching Optimality with Constant Feedback", ACM Mobihoc'16, Paderborn, Germany, July, 2016.

  22. J. Liu, A. Eryilmaz, N. B. Shroff, and E. Bentley, "Understanding the Impact of Limited Channel State Information on Massive MIMO Network Performances", ACM Mobihoc'16, Paderborn, Germany, July, 2016.

  23. L. Chen, F. Wu, J. Xu, K. Srinivasan, and N. B. Shroff, "BiPass: Enabling End-to-End Full Duplex," ACM Mobicom’17, Snowbird, Utah, Oct. 2017.

  24. J. Liu, A. Eryilmaz, N. B. Shroff, and E. S. Bentley, "Understanding the Impacts of Limited Channel State Information on Massive MIMO Cellular Network Optimization", IEEE Journal on Selected Areas in Communications (JSAC), vol. 35, no. 8, pp. 1715-1727, Aug. 2017.

  25. Z. Qian, F. Wu, Z. Zheng, K. Srinivasan, and N. B. Shroff, "Concurrent Channel Probing and Data Transmission in Full-duplex MIMO Systems", ACM Mobihoc'17, Chennai, India, Jul. 2017.

  26. M. Hashemi, C. E. Koksal, and N. B. Shroff, "Out-of-Band Millimeter Wave Beamforming and Communications to Achieve Low Latency and High Energy Efficiency in 5G Systems", IEEE Trans. on Communications (TCOM), vol. 66, no. 2, pp. 875-888, Feb. 2018.

  27. X. Du, Y. Sun, N. B. Shroff, and A. Sabharwal, "Reduced Latency via Scheduled Soft Full-duplex", submitted, 2018.

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