doc.: IEEE r1 Submission Novemebr 2005 C. Razzell, H. Waite (Philips)Slide 1 Project: IEEE P Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [Active Interference Cancellation for OFDM] Date Submitted: [ 14 November, 2005] Source: [C. Razzell] Company [Philips] Address [1151 McKay Drive, M/S SJ48A, San Jose, CA USA] Voice:[ ], FAX: [], + [H. Waite] Company [Philips] Address [1151 McKay Drive, M/S SJ48A, San Jose, CA USA] Voice:[ ], FAX: [], Re: [To be considered in context of TG3a down-selection] Abstract:[Tutorial and some early results on Active Interference Cancellation] Purpose:[To explain details of AIC for OFDM] Notice:This document has been prepared to assist the IEEE P 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 acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P

doc.: IEEE r1 Submission Novemebr 2005 C. Razzell, H. Waite (Philips)Slide 2 Introduction Flexible spectrum occupancy is a desirable attribute as recognized by the many TG3a presentations on Soft Spectrum Adaptation (SSA) Low complexity tone-nulling by simply deleting selected tones was previously considered state of the art. More recently, Active Interference Cancellation has been described in the literature. AIC will now be described further.

doc.: IEEE r1 Submission Novemebr 2005 C. Razzell, H. Waite (Philips)Slide 3 Reference Active interference cancellation technique for MB-OFDM cognitive radio Yamaguchi, H.; Microwave Conference, th European Volume 2, 13 Oct Page(s):1105 – 1108

doc.: IEEE r1 Submission Novemebr 2005 C. Razzell, H. Waite (Philips)Slide 4 OFDM notation Information in tones X(k) transformed into time domain samples x(n) If we upsample by a factor of 4 and perform the FFT, we obtain additional frequency domain resolution

doc.: IEEE r1 Submission Novemebr 2005 C. Razzell, H. Waite (Philips)Slide 5 Discrete spectrum values as function of transmitted tone values

doc.: IEEE r1 Submission Novemebr 2005 C. Razzell, H. Waite (Philips)Slide 6 Expressed in Matrix notation

doc.: IEEE r1 Submission Novemebr 2005 C. Razzell, H. Waite (Philips)Slide 7 Minimization Problem for nulling

doc.: IEEE r1 Submission Novemebr 2005 C. Razzell, H. Waite (Philips)Slide 8 MMSE solution W 2 is fixed for a given notch specification

doc.: IEEE r1 Submission Novemebr 2005 C. Razzell, H. Waite (Philips)Slide 9 Possible Simplifications

doc.: IEEE r1 Submission Novemebr 2005 C. Razzell, H. Waite (Philips)Slide 10 Considerations for upsampling and sin(x)/x compensation The above analysis assumes that the frequency domain response is entirely dictated by the mathematics of the transform process In fact, other factors such as sin(x)/x shaping due to the zero-order hold of the DACs Usually these filtering effects can be compensated in the frequency domain Any such frequency-domain compensation must be applied to the vector is performed

doc.: IEEE r1 Submission Novemebr 2005 C. Razzell, H. Waite (Philips)Slide 11 MATLAB® Simulation PSD [dBr] ~40dB notch

doc.: IEEE r1 Submission Novemebr 2005 C. Razzell, H. Waite (Philips)Slide 12 Simulation including upsampling and sin(x)/x correction

doc.: IEEE r1 Submission Novemebr 2005 C. Razzell, H. Waite (Philips)Slide 13 Analysis of Tx linearity to meet DAA requirements Approach –Simulate a AIC signal passing through a non-linear transmit model within Agilent ADS, and assess the degradation in notch depth as non-linearity is swept. BB signal includes nulling and active cancellation of sub-carriers #24 to #28 inclusive Resulting notch depth is 44 dB

doc.: IEEE r1 Submission Novemebr 2005 C. Razzell, H. Waite (Philips)Slide 14 Analysis of Tx linearity to meet DAA requirements ADS Test Bench Set up Generation of 528MHz spectrum with AIC notch Conversion to RF time domain signal and gain scaling to give required output power Modelling of TX RF non-linearity

doc.: IEEE r1 Submission Novemebr 2005 C. Razzell, H. Waite (Philips)Slide 15 Analysis of Tx linearity to meet DAA requirements AIC Input Signal with notch Total of 5 sub-carriers removed for AIC –Notch depth 44dB, absolute notch < -80dBm/MHz

doc.: IEEE r1 Submission Novemebr 2005 C. Razzell, H. Waite (Philips)Slide 16 Results Output Spectrum with TX linearity sweep –Notch depth is reduced as TX non-linearity increases Increasing Tx linearity

doc.: IEEE r1 Submission Novemebr 2005 C. Razzell, H. Waite (Philips)Slide 17 Results Output Spectrum with TX linearity sweep (zoom into notched part of spectrum) –Tx linearity swept in 1dB steps Input signal Output signal OIP3 =0dBm Output signal OIP3 =10dBm

doc.: IEEE r1 Submission Novemebr 2005 C. Razzell, H. Waite (Philips)Slide 18 Results Results Summary –“backoff” is a swept parameter of TX non-linearity –Pn_4103 indicates notch depth at the input (prior to non-linearity) –Ptx_n_4103 indicates notch depth at the output of the non-linear block –Notch delta indicates depth of output notch relative to input notch –Back-off = 0 corresponds to OIP3 = 0dBm –Back-off = 10 corresponds to OIP3 = 10dBm

doc.: IEEE r1 Submission Novemebr 2005 C. Razzell, H. Waite (Philips)Slide 19 Conclusions Computational complexity reduces to n aic vector dot products per IFFT –Computational cost looks reasonable Preliminary simulation results indicate that an OIP3 of +10dBm for the transmit path produces 40dB –RF implementation for a 30dB notch looks feasible Details on the impact of Tx DAC quantization can be found in the [Yamaguchi 2004] reference –Good performance with 2-4 bits of AIC tone precision Achieving the required notch depth at DC to cancel LO feedthrough still needs to be considered