Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [DSSS UWB Radio System] Date Submitted: [January 2005] Source: [Saeid Safavi and Ismail Lakkis ] Company [Wideband Access, Inc.] Address [10225 Barnes Canyon Road, Suite A209, San Diego, CA] Voice:[858-642-9114], FAX: [858-642-2037], E-Mail:[email@example.com] Re: [Response to Call for Proposals] Abstract: [This document describes Wideband Access Inc.’s approach for the TG4a alternate PHY] Purpose: [Preliminary Proposal for the IEEE802.15.4a Standard] 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. Safavi & Lakkis, Wideband Access, Inc.
Wideband Access, Inc.Preliminary Proposal for IEEE 802.15.4a Alternate PHY DSSS UWB Radio System Saeid Safavi & Ismail Lakkis Safavi & Lakkis, Wideband Access, Inc.
Proposal Summary • A robust direct sequence spread spectrum radio with large processing gains is proposed. • Despite its robustness the radio has a very simple and implementable architecture which is anticipated to support the size, cost and power consumption requirements of the altPHY. • Using DSSS, channel coding and a low receiver sensitivity, the system provides extended coverage beyond 30 m. • The radio design supports all of the technical requirements of TG4a. Safavi & Lakkis, Wideband Access, Inc.
Advantages • Simple Architecture: • Facilitates manufacturability and time to market • Low Power Consumption: • Low rate ADC • CMOS technology • Low Cost: • Single chip implementation • Small Size: • Compact architecture • Minimal usage of external components • Extended Range: • Large processing gain • Improved receiver sensitivity • FEC • Resistant to Interference, Multipath and Frequency Offsets • Proven Location Awareness Methodology Safavi & Lakkis, Wideband Access, Inc.
* System Block Diagram (Transmitter) Information Bits BPSK Mod & Channel Coding 4 Mcps BPF Short Code Spreading Differential Encoder A 125 kbps – 2 Mbps Radio Channel Modulated Long Code Generator 4 GHz (50 ppm) Integrator (Short Code Despreader) Channel Decoding & Data Detection Recovered Bits Integrator (Long Code Despreader) BPF LNA ADC Tb Differential Detector (Receiver) Modulated Long Code Generator 4 GHz (50 ppm) Safavi & Lakkis, Wideband Access, Inc.
1 5 7 8 9 4 2 3 10 6 Band Plan Future Development 3 dB BW = 1GHz Safavi & Lakkis, Wideband Access, Inc.
Distinctive Radio Features • Data Rates: Raw (125 kbps to 2 Mbps), Coded (250 kbps to 4 Mbps) • BW: 1.0 GHz (3.5 – 4.5 GHz) • Chip Rate: 1 Gcps • Local Oscillator Offset: 50 ppm • High Processing Gain: 24dB @ 4 Mb/s to 36 dB @ 250 kb/s • Link Margin: 6 dB gain over OOK • Extended Range: due to large processing gain, low sensitivity and FEC the range is larger than 30 m • Robust: robustness against noise and phase reversal errors, and high interference resistance due to large processing gain • Low Levels of Interference to other systems: due to the usage of DSSS with large processing gains • Single low-power CMOS chip • ADC operation at low rate (rather than chip rate) and Small SizeADC (1- 2 bit) • Simple and Cheap Implementation (no expensive components such as SAW filters, etc.) • Wide Dynamic Range • High Frequency Efficiency: due to efficient use of frequency within the band • Precise Ranging Procedure: based on TDOA • Simple, all digital Signal Acquisition and Synchronization • Support of large LO offsets: due to the differential detection Scheme • Support of Intra-cell mobility • Low Interchip Interference: an excellent code cross-correlation through usage of a subset of Kasami codes Safavi & Lakkis, Wideband Access, Inc.
Properties of Kasami Sequences • The small set of Kasami sequences is an optimal set of binary sequences with respect to the Welch Bound. • Long Code Spreading: • Sequence length: 255 • Number of possible sequences 16 • Max. Autocorrelation SLL: 17 • Max. Cross-correlation level: 17 • For lower data rates, a 2nd level of spreading (short code spreading) is introduced using pn-sequences & Kasami sequences (further increasing the processing gain). • If more codes are needed, the large set of Kasami codes can be used Safavi & Lakkis, Wideband Access, Inc.
Scalability Safavi & Lakkis, Wideband Access, Inc.
FEC • Viterbi convolutional FEC with constraint length K = 3, • Number of states = 4 Low complexity • Coding Gain > 3 dB • Requirement: • 1% PER for a 32 bytes packet (L = 256 bits) • PER @ L*BER BER @ 4e-5 • Without coding: EbN0 @ 8.9 dB • With coding: EbN0 @ 5.3 dB (3b), 5.8dB (2b) • Gain: Gain @ 3.6 dB Safavi & Lakkis, Wideband Access, Inc.
Link Budget Safavi & Lakkis, Wideband Access, Inc.
Simultaneously Operating Piconets • More channel can be identified with quasi-orthogonal spreading codes. • There are two levels of spreading which provide an extra degree of flexibility when defining system parameters for co-located piconets. • Kasami codes provide excellent cross-correlation properties which allows coexistence with other devices. Safavi & Lakkis, Wideband Access, Inc.
Coexistence and Interference Susceptibility • Due to the usage of a simple DSSS scheme with no frequency or time hopping, the interference to the neighboring systems is minimal (resulting in low levels of both instantaneous as well as average interference), satisfying the TG4a’s coexistence requirements • DSSS with large processing gain would also ensures robustness against interfering devices, hence a high interference susceptibility. Safavi & Lakkis, Wideband Access, Inc.
Location Strategy • The location strategy is based on Time Difference of Arrival (TDOA) using one-way ranging (OWR). This method involves measuring the time of arrival of a known signal from the mobile device at three or more reference (fixed) nodes. The location estimate is derived from the value of the Geometric Time Difference (GTD) between the time of arrivals at each node and a known time reference. • The server or controller node periodically broadcasts synchronization packets to the reference nodes. Each reference node captures the message packet it has received to a specific time resolution. The signals received at each fixed node is transmitted back to the controller node to give the time difference of arrival. Each of the time differences represent a location hyperbola that the mobile node can reside on (based on its TDOA). The intersection of two such hyperbolas are used to locate the position of the mobile in a 2D space. • Therefore, the position is calculated at the controller node location (based on hyperbolic trilateration). Safavi & Lakkis, Wideband Access, Inc.
dC – dB = dCB dA ,tA M dC ,tC Station of Interest (to be located) dB , tB dC – dA = dCA Location Strategy Fixed Node A C Fixed Node (TDOA) B Fixed Node Safavi & Lakkis, Wideband Access, Inc.
Conclusions • The DSSS system proposed herein is a simple and implementable radio that through its counter measures against fading, noise and interference can provide the robustness and extended range (well above 30 m) required by TG4a. • The location awareness methodology based on TDOA provides a precision ranging capability. • This system can be integrated in a compact CMOS chip with minimal external components and hence is a small-size, low-cost device. This combined with the radio robustness and location accuracy can support various 802.15.4a applications. • The simplicity and the proven modulation techniques used ensures feasibility and scalability of the radio. • FFD’s and RFD’s for different applications can be supported due to the scalability provided by a large set of spreading codes. Safavi & Lakkis, Wideband Access, Inc.