Sept 2005 doc IEEE 802 15 05 533

Sept 2005 doc. : IEEE 802. 15 -05 -533 r 0 Project: IEEE P 802. 15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [Motivation for Multi-band UWB] Date Submitted: [ 19 Sept, 2005] Source: [C. Razzell] Company [Philips] Address [1151 Mc. Kay Drive, M/S SJ 48 A, San Jose, CA 95131 -1706 USA] Voice: [ +1 408 474 7243], FAX: [], E-Mail: [charles. razzell@philips. com] Re: [To be considered in context of TG 3 a down-selection] Abstract: [Technical Contribution on pros and cons of Multi-band Approach to UWB] Purpose: [To inform and persuade] Notice: This document has been prepared to assist the IEEE P 802. 15. 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 802. 15. Submission 1 C. Razzell (Philips)

Sept 2005 doc. : IEEE 802. 15 -05 -533 r 0 What do we mean by multi-band? Multi-band UWB signaling is simply the division in the frequency domain of a single ultra-wideband signal into multiple sub-bands. Submission 2 C. Razzell (Philips)

Sept 2005 doc. : IEEE 802. 15 -05 -533 r 0 Parallel vs. Sequential Multiband Parallel Pulsed Multiband Submission Sequential Pulsed Multiband 3 C. Razzell (Philips)

Sept 2005 doc. : IEEE 802. 15 -05 -533 r 0 Sequential Multiband for Channel Isolation or for Modulation Capacity • Sequences can be fixed and used for piconet isolation or… • Variable and used to convey information (e. g. Spectral Keying™) Sequential Multiband with Sequence Keying Submission 4 C. Razzell (Philips)

Sept 2005 doc. : IEEE 802. 15 -05 -533 r 0 Spectrum Definition by pulse or otherwise • A further classification of multiband schemes needs to be made, namely between pulsed multiband OFDM multiband approaches – Pulsed multiband transmissions use a specifically chosen, constant pulse shape to obtain the frequency domain properties for each sub-band. – OFDM can be applied in each sub-band. The occupied bandwidth and spectral shape is largely defined by the inverse Fourier transform applied in the transmitter. This technique can be considered as further frequency division of each sub-band of the multiband scheme into a further parallel multiband scheme providing a much finer degree of granularity in the frequency domain. Submission 5 C. Razzell (Philips)

Sept 2005 doc. : IEEE 802. 15 -05 -533 r 0 Overall Classification Scheme for Multiband UWB OFDM Information -bearing (variable) Sequence PULSE Sequenced Multiband OFDM Piconet isolation (fixed) sequence Multiband PULSE OFDM MB-OFDM Scheme is highlighted Parallel Multiband PULSE Submission 6 C. Razzell (Philips)

Sept 2005 doc. : IEEE 802. 15 -05 -533 r 0 Detailed Motivation for Multi-band Approach to UWB Submission 7 C. Razzell (Philips)

Sept 2005 doc. : IEEE 802. 15 -05 -533 r 0 Outline of Discussion Points • Tight Control of Spectrum Mask • Receiver Sampling Rate Issues • Active Circuit Bandwidth and Power Consumption • ADC and DAC Sampling Rates • Robustness to Strong Narrow-band Interferers Submission 8 C. Razzell (Philips)

Sept 2005 doc. : IEEE 802. 15 -05 -533 r 0 Tight Control of Spectrum Mask • In-band spectrum flatness directly impacts link budget • Out-of-band attenuation requirements are likely to be tough, especially outside the US – Tight control is best achieved with digital filters for control and repeatability – Direct implementation of digital filters with >GHz sampling rates needed for single-band approach is impractical • Multi-band brings down sampling rates, allowing more digital filter implementation. Submission 9 C. Razzell (Philips)

Sept 2005 doc. : IEEE 802. 15 -05 -533 r 0 Example requirements for digital definition of Tx Spectrum • 1. 5 GHz Single-band UWB system – Baseband LP filters need at least 1. 5 GHz sampling rate in I and Q channels – Additional, non-trivial analog filters needed for removal of aliases • In view of these factors, single-band UWB system designers have sometimes resorted to purely analog filtering for pulse shaping. Submission 10 C. Razzell (Philips)

Sept 2005 doc. : IEEE 802. 15 -05 -533 r 0 Example requirements for digital definition of Tx Spectrum • 500 MHz per band multiband UWB system – Baseband LP filters need only 500 MHz sampling rate in I and Q channels – Excess bandwidth at the edges of the UWB spectrum is reduced by a factor N, where N is the number of sub-bands (since excess BW is given by B. a, where a is the raised cosine roll-off factor and B is the bandwidth of a sub-band). • Multi-band approach also allows the transmit power in each sub-band to be independently managed, for interference avoidance and overall in-band flatness compensation. Submission 11 C. Razzell (Philips)

Sept 2005 doc. : IEEE 802. 15 -05 -533 r 0 Receiver Sampling Rate Issues Required length of channel matched filter is product of excess delay in channel and the sampling rate Rate of multiply-accumulates is product of number of required taps and sampling rate Since Fs is proportional to receiver channel bandwidth, the square law proportionality with Fs (bandwidth) becomes a very significant factor in favor of processing one sub-band at a time per the multi-band approach Submission 12 C. Razzell (Philips)

Sept 2005 doc. : IEEE 802. 15 -05 -533 r 0 Active Circuit Bandwidth and Power Consumption In UWB receivers for sequential multiband modulation schemes, the first down-mixing step results in a bandwidth reduction by a factor equal to the number of sub-bands employed Submission 13 C. Razzell (Philips)

Sept 2005 doc. : IEEE 802. 15 -05 -533 r 0 Filter Feasibility • On-chip channel selectivity at baseband, is much more feasible in the multiband case, where the low-pass corner may be 250 MHz (for a total IF bandwidth of 500 MHz). • For the single-band case, the equivalent low-pass corner would have to be 750 MHz, which means that active on-chip filtering techniques are difficult if not impossible to apply. • Similarly, the current consumption required to obtain to linear operation and high dynamic range up to 250 MHz is much less than that required to reach 750 MHz. • Similar arguments apply to a direct up-conversion transmitter for similar reasons. Once again, the implementation difficulty is reduced for the analog transmitter blocks until the upconversion using an agile local oscillator spreads the bandwidth to its final value. Submission 14 C. Razzell (Philips)

Sept 2005 doc. : IEEE 802. 15 -05 -533 r 0 ADC and DAC Sampling Rates • The sampling rates required in the mixed signal components will obtain a reduction by a factor equal to the number of sub-bands employed – Useful considering the need for low power converters in portable applications – Higher precision converters may be used to provide dynamic range required for strong narrow-band interference Submission 15 C. Razzell (Philips)

Sept 2005 doc. : IEEE 802. 15 -05 -533 r 0 Vulnerability to Strong Interferers Two Strategies: • The receiver alone adapts by inserting erasures for the symbols to be received in the interference impacted sub-band • The transmitter and receiver negotiate to adopt a smaller or different set of sub-bands, avoiding the use the heavily interfered sub-band. Submission 16 C. Razzell (Philips)

Sept 2005 doc. : IEEE 802. 15 -05 -533 r 0 Multipath Energy Collection in Sequential Multiband Receivers Submission 17 C. Razzell (Philips)

Sept 2005 doc. : IEEE 802. 15 -05 -533 r 0 Fundamental Conflict • BPSK and QPSK modulation schemes are preferred for UWB, but limit uncoded data rate to R=2. PRF, where PRF is the pulse repetition frequency. • For sequential multiband good energy collection, using a single receive path, requires PRF 1/tch where tch is the excess delay of the channel • Assume tch=40 ns, then R 2/40 Gbps = 50 Mbps. – Realizing higher data rates for TG 3 a means sacrificing energy collection and consequently BER performance. • Require long dwell times on each band coupled with high information density not possible with simple pulses Submission 18 C. Razzell (Philips)

Sept 2005 doc. : IEEE 802. 15 -05 -533 r 0 Enter Multi-band OFDM • MB-OFDM benefits from all the generic multiband advantages described above, but… • The dwell time on each sub-band is 312. 5 ns • Energy collection period is up to 60. 6 ns • Number of uncoded bits per OFDM ‘pulse’ is up to 200, due to 100 data sub-carriers • Max uncoded data rate is 200/312. 5 Gbps = 640 Mbps. Submission 19 C. Razzell (Philips)

Sept 2005 doc. : IEEE 802. 15 -05 -533 r 0 Conclusions • Multiband techniques have a number of important implementation related advantages that have not been reviewed for a long time • Pulsed multiband disadvantages with respect to energy collection have been overcome by the adoption of OFDM in each sub-band • I hope that this review of the technical reasons to prefer the MB approach in general and MB-OFDM in particular has been helpful. Submission 20 C. Razzell (Philips)