1 / 52

Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: Chirp Spread Spectrum (CSS) PHY Presentation for 802.15.4a Date Submitted: January 04, 2005 Source: John Lampe Company: Nanotron Technologies Address: Alt-Moabit 61, 10555 Berlin, Germany

fadey
Download Presentation

Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: Chirp Spread Spectrum (CSS) PHY Presentation for 802.15.4a Date Submitted: January 04, 2005 Source: John Lampe Company: Nanotron Technologies Address: Alt-Moabit 61, 10555 Berlin, Germany Voice: +49 30 399 954 135, FAX: +49 30 399 954 188, E-Mail: j.lampe@nanotron.com Re: This is in response to the TG4a Call for Proposals, 04/0380r2 Abstract: The Nanotron Technologies Chirp Spread Spectrum is described and the detailed response to the Selection Criteria document is provided Purpose: Submitted as the candidate proposal for TG4a Alt-PHY 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. J. Lampe, R. Hach, L. Menzer, Nanotron

  2. Chirp Spread Spectrum (CSS)PHY Presentationfor 802.15.4a by John Lampe, Rainer Hach, and Lars Menzer Nanotron Technologies GmbHBerlin, Germany www.nanotron.com J. Lampe, R. Hach, L. Menzer, Nanotron

  3. CSS Proposal Presentation Contents • CSS System Overview • Channel Models & Simulation Results • Ranging • SCD Topics • Backward Compatibility • Clear Channel Assessment • Other Topics • PAR and 5C Requirement Checklist • Summary For more detail, please see our proposal, doc # 15-04-0689 J. Lampe, R. Hach, L. Menzer, Nanotron

  4. noise windowed windowed Sig A upchirp downchirp channel windowed windowed Sig B downchirp upchirp Logical Diagram of the Proposed System • Simplicity • Basically a 2 ary transmission system • The ‘windowed chirp’ is a linear frequency sweep with a total duration of 1 µs J. Lampe, R. Hach, L. Menzer, Nanotron

  5. Block-diagram Tx Digital Block Low-Pass Filter I/Q Modulator LP I fT = f ± 10 MHz LP Q LO f = 2.412, 2.437 or 2.462 GHz J. Lampe, R. Hach, L. Menzer, Nanotron

  6. Block-diagram Rx (Direct Conversion) 2 Low-Pass Filter I/Q Demodulator 3 DDDL 1 Up LP ADC I Down Digital Block LP ADC Q LO fR = fLO ± 10 MHz RSSI Chirp pulse 1 Correlation pulse 2 fLO = 2.412, 2.437 or 2.462 GHz Trigger signal with adaptive threshold 3 J. Lampe, R. Hach, L. Menzer, Nanotron

  7. Chirp Properties • Complex values of a windowed baseband up-chirp and down-chirp signals each with a total duration of 1µs • Flat magnitude • Plenty of roll-off time (easy to implement & meet regulatory requirements) • Significant simplification of correlator due to up-chirp and down-chirp similarities J. Lampe, R. Hach, L. Menzer, Nanotron

  8. Chirp Properties (cont.) • Up-converted up-chirp and down-chirp signals each with a total duration of 1µs J. Lampe, R. Hach, L. Menzer, Nanotron

  9. Chirp Properties (cont.) • Figure shows the autocorrelation function (ACF) of a chirp and cross-correlation function (CCF) of an up- and down-chirp • Note that the CCF has a constant low value (compared to DSSS sequences). J. Lampe, R. Hach, L. Menzer, Nanotron

  10. Chirp Properties (cont.) • This figure shows the PSD of the signal with a power of 10 dBm with 100 kHz resolution • At 12 MHz offset from the center is below -30dBm (which is the ETSI requirement for out of band emissions) J. Lampe, R. Hach, L. Menzer, Nanotron

  11. System Properties • Further processing of the signals Sig A and Sig B for symbol detection can be done either in a coherent (real part processing) or non-coherent manner (envelope filtering). • Since the analytical results are well known for AWGN channels we will mention these • Simulations over other channels will all refer to the non coherent system as drawn below. J. Lampe, R. Hach, L. Menzer, Nanotron

  12. System Properties (cont.) • This figure shows the analytical BER values for 2-ary orthogonal coherent and non coherent detection and the corresponding simulation results (1E7 symbols) for up down chirp (using the chirp signals defined above) • The performance loss due to the non-orthogonality of up and down chirps is very small. J. Lampe, R. Hach, L. Menzer, Nanotron

  13. Channel Models • Since this proposal refers to the 2.4GHz ISM band, only channel models with complete parameter sets covering this frequency range can be considered: • These are LOS Residential (CM1) and NLOS Residential (CM2). • The SCD requirements on the payload size to be simulated seem to be somewhat inconsistent. At some point 10 packets with 32 bytes are mentioned which would be a total of 2560 bits. On the other hand a PER of 1% is required which mean simulating much more than 100 packets or 25600 bits. • Accurate results are obtained when large number of independent transmissions of symbols are simulated. • BER is , with N = number bits. • For example, with PER=1% and N=256 (32 octets) we get BER=3.9258E-5 J. Lampe, R. Hach, L. Menzer, Nanotron

  14. Channel Model 1: LOS Residential J. Lampe, R. Hach, L. Menzer, Nanotron

  15. Channel Model 2: NLOS Residential J. Lampe, R. Hach, L. Menzer, Nanotron

  16. System Performance (CM2): PER • Transmit power of 10 dBm • 1 MBit / sec • No FEC J. Lampe, R. Hach, L. Menzer, Nanotron

  17. System Performance • Simulation over 100 channel impulse responses (as required in the SCD) were performed for channel model 1 and channel model 2. • No bit errors could be observed on channel model 1 (simulated range was 10 to 2000m). This is not really surprising because this model has a very moderate increase of attenuation over range (n=1.79) • The results for channel model 2 are presented. The parameter n=4.48 indicates a very high attenuation for higher ranges. The results were interpreted as PER respectively and for convenience were plotted twice (linear and log y scale). J. Lampe, R. Hach, L. Menzer, Nanotron

  18. Ranging Topics • TOA estimation • Dithering and Averaging • TOA processing • SDS TWR Technique • Error Sensitivity Analysis • Simulation Results J. Lampe, R. Hach, L. Menzer, Nanotron

  19. Approximate the impact of σu by: Assume the rising speed of the signal is proportional to the signal bandwidth: Since the power σ2 of band-filtered AWGN is proportional to the bandwidth we know that: Which leads to: TOA Estimation for Ranging Noise and Jitter of Band-Limited Pulse Given a band-limited pulse with noise σuwe want to estimate how the jitter (timing error) σt, is affected by the bandwidth B. Jitter can be represented as a variation in the rising edge of a pulse through a given threshold, J. Lampe, R. Hach, L. Menzer, Nanotron

  20. TOA Estimation for Ranging • The SN at the matched filter output is 2Es/N0 • If we assume a pulse with a rise time trise which is the inverse of the pulse bandwidth B (trise = 1/B) we can derive: • Bandwidth and signal to noise ratio can be traded against each other. J. Lampe, R. Hach, L. Menzer, Nanotron

  21. Principle of Dithering and Averaging pulse to transmit PHY packet to transmit Ti Ti • Dithering: transmitted pulse PHY packet transmitted t ΔTi1 ΔTi2 ΔTi3 ΔTin PHY packet received • Averaging: t ΔTiRX1 ΔTiRX2 ΔTiRX3 ΔTiRXn Ti Ti Ti Ti tToA’ J. Lampe, R. Hach, L. Menzer, Nanotron

  22. TroundA TreplyA Node A t Tprop Tprop Tprop Tprop Node B t TreplyB TroundB TOA Processing:Symmetrical Double-Sided Two-Way Ranging (SDS TWR) Tround... round trip time Treply... reply time Tprop... propagation of pulse Double-Sided: Each node executes a round trip measurement. Symmetrical: Reply Times of both nodes are identical (TreplyA =TreplyB). Results of both round trip measurements are used to calculate the distance. J. Lampe, R. Hach, L. Menzer, Nanotron

  23. total error due to clock TOA Processing:Effect of Time Base Offset Errors Assuming offset errors eA, eB of the timebases of node A and B we get: On the condition that the two nodes have almost equal behavior, we can assume: This has the effect that timebase offsets are canceled out: Calculations show that for 40 ppm crystals and 20 µs max difference between TroundA and TroundB and between TreplyA and TreplyB an accuracy below 1 ns can easily be reached! J. Lampe, R. Hach, L. Menzer, Nanotron

  24. Influence of Symmetry Error:Calculation of an SDS TWR Example System • Example system EtA = ±40 ppm, EtB = ±40 ppm (worst case combination): • A ΔTreplyof between 2 µs and 20 µsis typical for a low-cost implementation. • Implementations with symmetry error below 2 µs are feasible. • Conclusion: Even a 20 µs symmetry error allows excellentsingle-pulse accuracy of distance. J. Lampe, R. Hach, L. Menzer, Nanotron

  25. Simulation of a SDS TWR System Example system: Simulates SDS TWR + Dithering & Averaging Crystal Errors ±40 ppm Single shot measurements @ 1 MBit/s data rate (DATA-ACK) Transmit Jitter = ± 4 ns (systematic/pseudo RN-Sequence) Pulse detection resolution = 4 ns Pulses averaged per packet = 32 Symmetry error = 4 µs (average) Distance = 100 m Results of Distance Error ∆d: |∆dWC| < 50 cm |∆dRMS| < 20 cm J. Lampe, R. Hach, L. Menzer, Nanotron

  26. Selection Criteria Document Topics J. Lampe, R. Hach, L. Menzer, Nanotron

  27. Backward Compatibility Option • Due to the similarities with DSSS it is possible to implement this proposal in a manner that will allow backward-compatibility with the 802.15.4 2.4 GHz standard. • The transmitter changes are relatively straightforward. • Changes to the receiver would include either dual correlators or a superset of CSS and DSSS correlators. • Optional methods for backward-compatibility could be left up to the implementer • mode switching • dynamic change (on-the-fly) technique • This backward-compatibility would be a significant advantage in the marketplace by allowing these devices to communicate with existing deployed 802.15.4 infrastructure and eliminating customer confusion. J. Lampe, R. Hach, L. Menzer, Nanotron

  28. Signal Robustness • The proposed CSS PHY is designed to operate in a hostile environment • Multipath • Narrow and broadband intentional and unintentional interferers • Since a chirp transverses a relatively wide bandwidth it has an inherent immunity to narrow band interferers • Multipath is mitigated with the natural frequency diversity of the waveform • Broadband interferer effects are reduced by the receiver’s correlator • Forward Error Correction (FEC) can further reduce interference and multipath effects. • Three non-overlapping frequency channels in the 2.4 GHz ISM band • This channelization allows this proposal to coexist with other wireless systems such as 802.11 b, g and even Bluetooth (v1.2 has adaptive hopping) via DFS • CSS proposal utilizes CCA mechanisms of Energy Detection (ED) and Carrier Detection • These CCA mechanisms are similar to those used in IEEE 802.15.4-2003 • In addition to the low duty cycle for the applications served by this standard sufficient arguments were made to convince the IEEE 802 sponsor ballot community that coexistence was not an issue. J. Lampe, R. Hach, L. Menzer, Nanotron

  29. Support for Interference Ingress • Example (without FEC): • Bandwidth B of the chirp = 20 MHz • Duration time T of the chirp = 1 µs • Center frequency of the chirp (ISM band) = 2.437 GHz • Processing gain, BT product of the chirp = 13 dB • Eb/N0 at detector input (BER=10E-4) = 12 dB • In-band carrier to interferer ratio (C/I @ BER=10-4)= 12 - 13 = -1 dB • Implementation Loss = 2 dB J. Lampe, R. Hach, L. Menzer, Nanotron

  30. Support for Interference Egress • Low interference egress • IEEE 802.11b receiver • More than 30 dB of protection in an adjacent channel • Almost 60 dB in the alternate channel • These numbers are similar for the 802.11g receiver J. Lampe, R. Hach, L. Menzer, Nanotron

  31. Regulatory • Devices manufactured in compliance with the CSS proposal can be operated under existing regulations in all significant regions of the world • Including but not limited to North and South America, Europe, Japan, China, Korea, and most other areas • There are no known limitation to this proposal as to indoors or outdoors • The CSS proposal would adhere to the following worldwide regulations: • United States Part 15.247 or 15.249 • Canada DOC RSS-210 • Europe ETS 300-328 • Japan ARIB STD T-66 J. Lampe, R. Hach, L. Menzer, Nanotron

  32. Scalability: Data Rate • Mandatory rate = 1 Mb/s • Optional rate = 267 Kb/s • Other possible data rates include 2 Mb/s to allow better performance in a burst type, interference limited environment or a very low energy consumption application • Lower data rates achieved by using interleaved FEC • Lower chirp rates would yield better performance • longer range, less retries, etc. in an AWGN environment or a multipath limited environment • It should be noted that these data rates are only discussed here to show scalability, if these rates are to be included in the draft standard the group must revisit the PHY header such as the SFD. J. Lampe, R. Hach, L. Menzer, Nanotron

  33. Scalability: Frequency Bands • The proposer is confident that the CSS proposal would also work well in other frequency bands • Including the 5 GHz UNII / ISM bands J. Lampe, R. Hach, L. Menzer, Nanotron

  34. Scalability: Data Whitener • Additionally, the group may consider the use of a data whitener, similar to those used by Bluetooth and IEEE 802.11 to produce a more “noise-like” spectrum and allow better performance in synchronization and ranging. J. Lampe, R. Hach, L. Menzer, Nanotron

  35. Scalability: Power Levels • For extremely long ranges the transmit power may be raised to each country’s regulatory limit, for example: • The US would allow 30 dBm of output power with up to a 6 dB gain antenna • The European ETS limits would specify 20 dBm of output power with a 0 dB gain antenna • Note that even though higher transmit power requires significantly higher current it doesn’t significantly degrade battery life since the transmitter has a much lower duty cycle than the receiver, typically 10% or less of the receive duty cycle. J. Lampe, R. Hach, L. Menzer, Nanotron

  36. Simultaneous Operating Piconets • Separating Piconets by frequency division • This CSS proposal includes a mechanism for FDMA by including the three frequency bands used by 802.11 b, g and also 802.15.3 • It is believed that the use of these bands will provide sufficient orthogonality • The proposed chirp signal has a rolloff factor of 0.25 which in conjunction with the space between the adjacent frequency bands allows filtering out of band emissions easily and inexpensively. J. Lampe, R. Hach, L. Menzer, Nanotron

  37. Clear Channel Assessment • A combination of symbol detection (SD) and energy detection (ED) has proven to be useful in practice (e.g. 802.11x, 802.15.4). • CCA is used by the 15.4 MAC to significantly increase the number of active nodes possible by reducing the probability of collisions. J. Lampe, R. Hach, L. Menzer, Nanotron

  38. MAC Enhancements and Modifications • There are very minimal anticipated changes to the 15.4 MAC to support the proposed Alt-PHY. • Three channels are called for with this proposal and it is recommended that the mechanism of channel bands from the proposed methods of TG4b be used to support the new channels. • There will be an addition to the PHY-SAP primitive to include the choice of data rate to be used for the next packet. This is a new field. • Ranging calls for new PHY-PIB primitives are expected to be developed by the Ranging subcommittee. J. Lampe, R. Hach, L. Menzer, Nanotron

  39. Frame Structure • The SFD structure has different values for, and determines, the effective data rate for PHR and PSDU • The Preamble is 32 bits in duration (a bit time is 1 µs) • In this proposal, the PHR field is used to describe the length of the PSDU that may be up to 256 octets in length • In addition to the structure of each frame, the following shows the structure and values for frames including overhead not in the information carrying frame J. Lampe, R. Hach, L. Menzer, Nanotron

  40. Throughput 797 Kb/s 330 Kb/s 245 Kb/s 155 Kb/s 267 Kb/s plot 1 Mb/s plot Tack= 192 µs SIFS= 192 µs J. Lampe, R. Hach, L. Menzer, Nanotron

  41. Signal Acquisition • Although CSS could use a shorter preamble, for consistency with IEEE 802.15.4-2003 this CSS proposal is based upon a preamble of 32 symbols which at 1MS/s is 32 µs • Existing implementations demonstrate that modules, which might be required to be adjusted for reception (gain control, frequency control, peak value estimation, etc.), can settle in this time J. Lampe, R. Hach, L. Menzer, Nanotron

  42. Link Budget footnotes [1] Rx noise figure: in addition the proposer can select other values for special purpose (e.g. 15 dB for lower cost lower performance system) [2] The minimum Rx sensitivity level is defined as the minimum required average Rx power for a received symbol in AWGN, and should include effects of code rate and modulation. J. Lampe, R. Hach, L. Menzer, Nanotron

  43. Communication No system inherent restrictions are seen for this proposal The processing gain of chirp signals is extremely robust against frequency offsets such as those caused by the Doppler effect when there is a high relative speed vrel between two devices. The Doppler effect must also be considered when one device is mounted on a rotating machine, wheel, etc. The limits will be determined by other, general (implementation-dependent) processing modules (AGC, symbol synchronization, etc.). Ranging The ranging scheme proposed in this document relies on the exchange of two hardware acknowledged data packets One for each direction between two nodes The total time for single-shot (2 data, 2 Ack) ranging procedure between the two nodes is the time trangingwhich, depending on the implementation, might be impacted by the uC performance. During this time the change of distance should stay below the accuracy da required by the application. The worst case is: For da = 1m tranging= 2 ms this yields vrel << 1000 m/s Mobility Values J. Lampe, R. Hach, L. Menzer, Nanotron

  44. Power Management Modes • Power management aspects of this proposal are consistent with the modes identified in the IEEE 802.15.4: 2003 standard • There are no modes lacking nor added • Once again, attention is called to the 1 Mbit/s basic rate of this proposal and resulting shorter “on” times for operation J. Lampe, R. Hach, L. Menzer, Nanotron

  45. Power Consumption The typical DSSS receivers, used by 802.15.4, are very similar to the envisioned CSS receiver • The two major differences are the modulator and demodulator • The power consumption for a 10 dBm transmitter should be 198 mW or less • The receiver for the CSS is remarkably similar to that of the DSSS with the major difference being the correlator • The difference in power consumptions between these correlators is negligible so the power consumption for a 6 dB NF receiver should be 40 mW or less • Power save mode is used most of the time for this device and has the lowest power consumption • Typical power consumptions for 802.15.4 devices are 3 µW or less • Energy per bit is the power consumption divided by the bit rate • The energy per bit for the 10 dBm transmitter is less than 0.2 µJ • The energy per bit for the receiver is 60 nJ • As an example, the energy consumed during an exchange of a 32 octet PDU between two devices would be 70.6 µJ for the sender and 33.2 µJ for the receiver J. Lampe, R. Hach, L. Menzer, Nanotron

  46. Antenna Practicality • The antenna for this CSS proposal is a standard 2.4 GHz antenna such as widely used for 802.11b,g devices and Bluetooth devices. • These antennas are very well characterized, widely available, and extremely low cost. • Additionally there are a multitude of antennas appropriate for widely different applications. • The size for these antennae is consistent with the SCD requirement. J. Lampe, R. Hach, L. Menzer, Nanotron

  47. Size and Form Factor • The implementation of the CSS proposal will be much less than SD Memory at the onset • Following the form factors of Bluetooth and IEEE 802.15.4 / ZigBee • The implementation of this device into a single chip is relatively straightforward • As evidenced in the “Unit Manufacturing Complexity” slides J. Lampe, R. Hach, L. Menzer, Nanotron

  48. Unit Manufacturing Complexity • Target process:RF-CMOS, 0.18 µm feature size J. Lampe, R. Hach, L. Menzer, Nanotron

  49. Unit Manufacturing Complexity • Target process:RF-CMOS, 0.13 µm feature size J. Lampe, R. Hach, L. Menzer, Nanotron

  50. Time To Market • No regulatory hurdles • CSS-based chips are available on the market • No research barriers – no unknown blocks • Normal design and product cycles will apply • Can be manufactured in all CMOS J. Lampe, R. Hach, L. Menzer, Nanotron

More Related