IEEE P802.22 Wireless RANs Date: 2006-01-18 January 2006 doc.: IEEE 802.22-06/xxxxr0 January 2006 Uplink Channel Sounding for Enabling Closed-Loop Transmit Antenna Array Techniques IEEE P802.22 Wireless RANs Date: 2006-01-18 Authors: Notice: This document has been prepared to assist IEEE 802.22. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.22. Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures http://standards.ieee.org/guides/bylaws/sb-bylaws.pdf including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chair Carl R. Stevenson as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802.22 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at patcom@iee.org. > F. W. Vook, Motorola Labs F. W. Vook, Motorola Labs

January 2006 doc.: IEEE 802.22-06/xxxxr0 January 2006 Abstract This contribution describes a signaling methodology called Uplink Channel Sounding (ULCS) which is an effective means for providing channel response information to a base station antenna array in Time Division Duplexing (TDD) systems. Uplink Channel Sounding enables a wide variety of closed-loop transmit antenna array techniques such as adaptive beamforming, downlink Spatial Division Multiple Access, and closed-loop Multiple Input Multiple Output (MIMO). A version of ULCS is currently used in the IEEE 802.16e standard for Mobile Broadband Wireless Access and recently has been included in the release 1 system profiles for mobile WiMAX systems. Enabling closed-loop transmission techniques such as beamforming and SDMA can significantly increase system capacity, which is essential for a competitive 802.22 standard. F. W. Vook, Motorola Labs F. W. Vook, Motorola Labs

What is UL Channel Sounding? January 2006 What is UL Channel Sounding? UL Channel Sounding is a means of providing channel response information to the BS on an as-needed basis CPE transmits sounding waveform on the UL to enable the BS to measure the channel response Intended for TDD systems where UL&DL RF reciprocity can be leveraged Simple, efficient, low complexity, and effective Adopted in IEEE 802.16e Adopted in current draft of the Release 1 WiMAX profile for Mobile Broadband Wireless F. W. Vook, Motorola Labs

What does UL Channel Sounding Enable? January 2006 What does UL Channel Sounding Enable? ULCS enables all types of Closed-Loop Transmit Antenna Array Techniques on the DL in TDD: Baseband digital transmit beamforming A.K.A.: Transmit adaptive array, max-ratio transmission (MRT), eigenbeamforming (EBF), closed-loop precoding, etc. TX-Spatial Division Multiple Access (SDMA) A.K.A.: Multi-user spatial multiplexing / Concurrent transmissions / Multi-user beamforming, etc. CL-Multiple Input Multiple Output (MIMO) A.K.A.: Multi-stream transmit beamforming, spatial multiplexing, etc. ULCS provides an easier and better-performing alternative to the other 802.16e Closed-Loop MIMO techniques with minimal added complexity to the CPE Lower channel measurement delay Better frequency-response tracking F. W. Vook, Motorola Labs

Baseband Digital Transmit Beamforming January 2006 Baseband Digital Transmit Beamforming Beamforming on OFDM subcarriers: Transmit Adaptive Array (TXAA) Max Ratio transmission (MRT) Closed-Loop Precoding Eigenbeamforming Etc. Benefits: Increases the SNR and capacity of the data channels Robust to multipath scattering Fading mitigation in scattered channels Diagram for the kth OFDM subcarrier: F. W. Vook, Motorola Labs

Spatial Multiplexing Transmission January 2006 Spatial Multiplexing Transmission Multi-stream baseband digital transmit beamforming TX-SDMA CL-MIMO MIMO Precoding Etc. Diagram for the kth OFDM subcarrier: F. W. Vook, Motorola Labs

How does UL Channel Sounding Operate? (1/3) January 2006 How does UL Channel Sounding Operate? (1/3) Presence and characteristics of “Sounding Zone” can be signaled in a DL Control message The BS commands one or more CPEs to transmit a “Sounding Waveform” in the Sounding Zone Only used when needed Periodicity feature can be used to significantly reduce sounding-command-IE overhead if continual sounding is required Multiple CPE sounding waveforms can be multiplexed on the same time-frequency sounding resources F. W. Vook, Motorola Labs

How does UL Channel Sounding Operate? (2/3) January 2006 How does UL Channel Sounding Operate? (2/3) During sounding, the BS measures channel response with standard channel estimation techniques Sounding waveform can be configured to match the frequency occupancy of the upcoming DL transmission Can be configured to match the upcoming downlink allocation Efficient simultaneous multiplexing of multiple users in each sounding symbol interval Decimation separability Orthogonal sequence separability F. W. Vook, Motorola Labs

How does UL Channel Sounding Operate? (3/3) January 2006 How does UL Channel Sounding Operate? (3/3) For DL transmissions: Dedicated pilots on DL enable aggregate channel estimation at the CPE CPE uses only the pilots unique to its allocation For TX-Beamforming, single-antenna allocations can be used to schedule data transmissions For TX-SDMA and CL-MIMO, the multi-user/stream allocation methodologies can be used F. W. Vook, Motorola Labs

Multiplexing Multiple CPE Sounding Waveforms January 2006 Multiplexing Multiple CPE Sounding Waveforms Two Methods for enabling optimum multi-source channel estimation on the same time-frequency sounding resources: Decimation Separability Multiple CPEs share the same sounding allocation, but occupy orthogonal subcarriers Each CPE occupies every Dth subcarrier, but with a different offset value Useful in low SNR scenarios Sequence Separability Multiple CPEs share the same sounding allocation and occupy the same subcarriers Each CPE transmits the same underlying sequence, but with a CPE-dependent frequency domain phase ramp Useful in higher SNR scenarios F. W. Vook, Motorola Labs

ULCS: Comparisons with other 802.16e techniques January 2006 ULCS: Comparisons with other 802.16e techniques TXAA enabled with UL Channel Sounding performs better than all other 802.16e single-stream closed-loop feedback-oriented approaches => Provides higher throughputs at lower SNR Four base antennas Single data stream transmitted to a single SS on the downlink Broadband downlink (i.e., PUSC) Ideal channel knowledge during downlink reception UL Channel Sounding: Uplink SNR=0 dB during sounding 8 Mobiles simultaneously sound the full band (to show efficiency of UL sounding waveform design) Realistic channel estimation performed during UL sounding Spatial Channel: 2 usec RMS channel with 15 degree angular spread at the base station 0 MPH 802.16e techniques: Codebook, selection, and grouping use 802.16 CQI feedback channel CQI feedback is limited to the equivalent of a single OFDM symbol so that the overhead is the same as sounding (for fair comparisons) Codebook, selection, and grouping track the frequency selectivity as best they can given the fixed amount of feedback Other 802.16e closed-loop techniques TXAA enabled with UL Channel Sounding Single Tx antenna F. W. Vook, Motorola Labs

Summary of UL Channel Sounding Advantages January 2006 Summary of UL Channel Sounding Advantages Enables Closed-Loop Antenna Array transmission such as Beamforming, MIMO, and SDMA on the downlink Higher link capacities, higher per-user and per system throughputs, less interference to other cells Feedback methods cannot support TX-SDMA on DL Less channel measurement latency in TDD systems compared to feedback methods Important in vehicular applications, but also in fixed-access SDMA transmissions Future-Proof: Transmit array algorithms can be upgraded at the BS with no impact on CPE Technique is independent of the number of BS antennas Small impact on CPE: Complexity is in the BS rather than CPE (unlike a feedback methodology) Dedicated pilots for CPE DL channel estimation Easier Channel Estimation problem compared with Feedback approaches For 4 antenna BS: four single-source channel estimation versus one four-source channel estimation Current standard won’t support estimating > 4 antennas for feedback methods. Handles asymmetric bandwidth occupancy of UL&DL transmissions Helpful when UL data cannot be used to derive the complete channel response Highly efficient waveform design allows for multiplexing multiple sounding waveforms from many users on the same sounding resources Waveforms configurable to support both low SNR uplink conditions and high delay spread scenarios – under control of BS F. W. Vook, Motorola Labs

January 2006 References IEEE 802.16e/D12 - Draft IEEE Standard for Local and Metropolitan area Networks – Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems – Amendment for Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands, Institute of Electrical and Electronic Engineers, New York, NY, USA, October 2005. IEEE C802.16e-04/103r2, “Signaling Methodologies to Support Closed-Loop Transmit Processing in TDD-OFDMA,” 7/07/2004 IEEE C802.16e-04/263r3, “Uplink Channel Sounding for TDD OFDMA,” 8/31/2004 F. W. Vook, Motorola Labs