Non-Coherent Ranging Receiver with Coherent Pulse Compression

1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks Submission Title: [A Non Coherent Ranging Receiverwith Coherent Pulse Compression] Date Submitted: [June 2005] Source: [Gidi Kaplan, Dan Raphaeli] Company [SandLinks Ltd.] Address [Hanehoshet 6 Tel Aviv Israel] Voice:[], E-Mail: [danr@eng.tau.ac.il] Re: [] Abstract: [] Purpose: [Contribution to 802.15 TG4a] Notice: This document has been prepared to assist the IEEE P802.15. 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 P802.15.

2. A Non Coherent Ranging Receiverwith Coherent Pulse Compression Gidi Kaplan & Dani Raphaeli Sandlinks June 3rd, 05

3. Terminology • [Terminology - as agreed lately over the reflector] • Pulse – a single UWB pulse (on the order of 1-2 nsec) • Burst – a sequence of ‘L’ UWB pulses (each pulse possibly modulated, the whole sequence has some ‘code’). Possibly, L may be between 11 to 33. • Symbol - for data or ranging – comprises of M bursts. • Each pulse has energy of Ep= Es/(L*M) where Es is the symbol energy.

4. The Basic Idea • Non-Coherent (NC) ranging (and demodulation) is considered in 802.15.4a, due to lower degree of complexity vs. a Coherent Receiver • The basic NC receiver employs an energy detector over each UWB pulse. It suffers a considerable ‘Squaring Loss’ due to the inherently small Ep/No. • Here, we suggest a receiver which gets the full ‘processing gain’ from each Burst of UWB pulses (before a square-law operation). • It is more complex than the ‘conventional’ NC receiver, but it allows a tradeoff of complexity vs. performance.

5. The basic idea (cont.) • Assume that the receiver employs a (complex) down conversion to baseband in its front-end; thus all subsequent discussion is in complex baseband. • We further assume that over the burst, the pulses are bi-phase modulated, according to a ‘pulse compression code’. • The latter should have a good autocorrelation; the choice of the sequence is a different issue, not discussed here.

6. Correlation over the Burst • The receiver employs a correlator over the (short) burst, and effectively sums up the UWB pulses in a coherent manner (note for ranging: a correlator has a known delay). • To get the symbol energy, the receiver – in principle- sums up the squares (energies) of the bursts. • Note, the receiver does not employ a phase locked loop to track the carrier phase • If the burst is short enough, then even with a low accuracy crystal, the total phase difference (over the burst) is small. • As an example, if the burst lasts over 200nsec, and there is 100ppm difference in freq between Tx. And Rx, the phase difference is less than 10 degree for Fc=4Ghz.

7. NC ranging receiver • For ranging, the receiver has to sum up the energies of many bursts (taking care of the delay between successive bursts), in order to obtain a good E/N for the averaged pulse. • It may do so by using a bank of K ‘energy detectors’, where each one is over D=2nsec (as an example), and the ‘bank’ covers some time window to account for the multipath energy spread. • In this manner, the receiver gets an ‘equivalent’ squared pulse, which actually has K energy level, one for each window of D nsec (from time 0 till D*K nsec); • The ranging algorithm compares the energy detector levels to a threshold in order to find the first cluster arrival time.

8. An Example • Suppose each (ranging) symbol is composed of two bursts of UWB pulses, each one of relatively short length d1 (what we call also ‘active time’) followed by an interval of ‘quiet time’ d2. • The total symbol length is then 2*(d1+d2). • For each burst, the receiver will employ a ‘coherent’ correlations operation, then detect the energy (using a bank of d1/D energy detectors) of the resultant pulse; • It then has to sum up the two energy banks results (with the proper delays). • This operation is done over ‘N’ symbols, as required (by analysis or simulation) to get the required ranging error for a given link. • In this case the squaring loss suffered is due to squaring of half the symbol (with 0.5Es/No). • The following diagram is a (very basic) block diagram of the receiver.

9. An example (two bursts per symbol)