Interference Mitigation using Conjugate Data Repetition IEEE Presentation Submission Template (Rev. 9) Document Number: IEEE S80216m-08_595 Date Submitted: Source: Kiran Kuchi, J Klutto Milleth, Vinod Ramaswamy, Padmanabhan Suryasarman, Baskaran Dhivagar, K Giridhar, Bhaskar Ramamurthi CEWiT India Venue: Denver, USA Purpose: To facilitate the choice of interference mitigation schemes during the IEEE meeting in Denver, USA Notice: This document does not represent the agreed views of the IEEE Working Group or any of its subgroups. It represents only the views of the participants listed in the “Source(s)” field above. It is offered as a basis for discussion. It is not binding on the contributor(s), who 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 Patent Policy: The contributor is familiar with the IEEE-SA Patent Policy and Procedures: and. Further information is located at and.

Outline Motivation Interference Suppression – Conjugate data repetition Orthogonal pilots Results and proposed SDD text 4/15/2015CEWiT Confidential Information2

Interference Suppression Poor cell edge link budget in reuse-1 networks – In urban deployments in India, typical cell size has m radius – Interference limited in both uplink and downlink – Severe co-channel interference (CCI) – Multiple CCI up to 3-dominant interferers 2-antenna MMSE receiver can reject only a single dominant CCI Existing solutions – DL control uses rate ½ QPSK and bit-level data repetition up to 6-times Yet, poor downlink control channel coverage – At cell edge, UL also supports rate ½ QPSK and data repetition up to 6-times – Significant loss in spectrum efficiency

Interference Mitigation Using Conjugate Data Repetition (CDR) 4/15/20154CEWiT Confidential Information

Conjugate Data Repetition (CDR) Conjugate symbol repetition across adjacent subcarriers After complex de-conjugation, the receiver has two copies of signal and interference with different channel states – 2-antenna MMSE can suppress 3 dominant CCI – An advanced receiver can reject up to 4 dominant CCI The proposal is suitable for common control channels which are always transmitted in predetermined locations Conjugate repetition is applied in localized slots of deterministic size – Slots are distributed in entire frequency in diversity mode More flexible slot allocation compared to Panasonic proposal C802.16m-07/211 BS-1BS-2 F1Y1 F2Y1* F3Y2 F4Y2* F5P2 F6Y3 F7Y3* F8Y4 F9Y4* F1X1 F2X1* F3X2 F4X2* F5P1 F6X3 F7X3* F8X4 F9X4*

Conjugate Data Repetition T1T2T3T4 X1X5X5*X1* X2X6X6*X2* P1X7X7*P2 X3X8X8*X3* X4X9X9*X4* T1T2T3T4 Y1Y5Y5*Y1* Y2Y6Y6*Y2* P3Y7Y7*P4 Y3Y8Y8*Y3* Y4Y9Y9*Y4* BS-1BS-2 In this example, pairs of conjugate data symbols are repeated in the same subcarrier but in different OFDM symbols The concept can be applied to both control and data regions For repetition factors greater than 2, a deterministic or random phase rotation is applied in addition to conjugation 2D-POD is the preferred OL transmit diversity mode The IC receiver works in virtual (single) antenna mode

Conjugate Data Repetition Basic Idea – Each BS transmits data in conjugate symbol pairs on a pair of subcarriers – 1 st BS transmits – 2 nd BS transmits – Complex-conjugation on – After complex de-conjugation, the receiver has two copies of signal and interference with different channel states Signal Interference – Receiver jointly filters – At cell edge, 2-antenna MMSE can suppress up to 8 CCI with non-uniform power profile

Simulation Results with 3-Dominant CCI LOS Channel Flat Fading

Cell Edge Performance with 8-Interferers 4/15/2015CEWiT Confidential Information9 SINR of MMSE receiver with conjugate repetition in flat fading channel, 8-interferers, SNR=30 dB, input SINR=-7 dB Interference Profile Interference power I0I0 0 I1I I2I I3I I4I I5I I6I I7I

Pilot Support Reference to S80216m-08_296r1.ppt S80216m-08_296r1.ppt

Quasi Orthogonal Pilot Design With PN pilots – Poor channel estimation quality and reduced interference rejection gain We prefer pilots colliding with pilots – A cluster is defined as a collection of a group of sectors The group may be formed with sectors from same cell or different cells – Same PN cover with orthogonal pilot codes with in a cluster Within a cluster, interferers will have orthogonal pilots At cluster boundaries, some interferers may have non-orthogonal pilots – Different PN sequences in adjacent clusters

Quasi Orthogonal Pilots Cluster Pattern-1 – Each cell has three sectors employing different orthogonal codes which are having the same color. These three sectors forms a cluster which use the same PN sequence or share the same pilot locations – Different colors depict different clusters which use different PN cover or shifted pilot locations Cluster Pattern-2 – A cluster is formed by grouping sectors from adjacent cells. Sectors in the same cluster use the same color Cluster Pattern-1 Cluster Pattern-2

Quasi Orthogonal Pilots 2D-MMSE channel estimation on slot by slot Near interference free channel estimation With 2-receiver antennas, and conjugation repetition, cell edge interference rejection up to 8- interferers Significant gain in system performance

Link simulation with Quasi-Orthogonal Pilots 4/15/2015CEWiT Confidential Information14 Simulation Assumptions PED-A channel Localized allocation RB size 9x6 ½ QPSKwith 360 bits 2Tx 2Rx 2D-POD transmit diversity Total pilot density 11.11% Quasi-orthogonal pilots Interference power profile [ ] dB Rest of the interference is modeled as AWGN Conjugate repetition factor=2 SNR is defined as signal to rest of the interference power

CDF of BLER of Cell Edge User Interference power profile in dB [ ] 4/15/2015CEWiT Confidential Information15 Simulation Assumptions PED-B channel Distributed allocation RB size 9x6 ½ QPSK with 360 bits 2Tx 2Rx 2D-POD transmit diversity Total pilot density 11.11% Quasi-orthogonal pilots Rest of the interference is modeled as AWGN SNR= 35 dB SIR=-3 dB Conjugate repetition factor=2 SNR is defined as signal to rest of the interference power This is a preliminary result with few simulation runs Trend shows that quasi-orthogonal pilots (Walsh+PN cover) gives a high advantage over PRBS pilots

Conclusion We propose data repetition in conjugate pairs – Flexible slot allocation High interference suppression using MMSE Suitable for common control channel – With 2D Phase Offset Diversity (2D-POD) For data channels, this scheme shall be used in a cell edge FFR zone – Better spectrum efficiency compared to 1/3 reuse 4/15/2015CEWiT Confidential Information16

Proposed SDD text Interference mitigation techniques using conjugate data repetition (CDR) shall be supported for data and common control channels. CDR includes simple repetition of modulated data. Use sector specific orthogonal and quasi- orthogonal pilots 4/15/2015CEWiT Confidential Information17