Merlion L & S Band System

Under the MERLION project name, Nanyang Technological University of Singapore has teamed up with Surrey Satellite Technology Ltd. of the UK and developed a sophisticated communication payload on the UoSAT-12 mini-satellite which was launched recently. The MERLION payload combines an analogue and digital regenerative transponder, with L-band uplink and S-band downlink. The transponder can be configured in-orbit for a variety of functions and experiments, and carries dual signal processors. The digital uplink comprises a frequency agile L-band receiver, and 9600bps FSK and IMbps BPSK demodulators. The frequency agile digital S-band downlink is intended for high speed data transfer and will be employed to perform a variety of communication experiments. It is also capable of low bit rate spread spectrum communications, together with convolutional coding options to investigate its performance in the highly dynamic environment of LEO. The downlink can be configured to perform link characterisation at these frequencies. In conjunction with the 80386EX based On-Board-Computers, the digital uplink and downlink system can be configured into a high rate Store-and-Forward transponder. This paper would introduce the basic Medion architecture and design considerations, to realise the above functionality within the scope of a low cost mission

Indoor positioning using UWB-IR signals in the presence of dense multipath with path overlapping

This paper presents a method for positioning using ultra-wideband impulse radio (UWB-IR) signals that is robust in indoor environments characterized by dense multipath channel with path overlapping. Path overlapping effects arising from multipath in dense cluttered environments decrease the direct path resolution in time domain, and hence induce time-of-arrival (TOA) and angle-of-arrival (AOA) based positioning inaccuracy. To mitigate this problem, system design that is capable of resolving the closely-spaced multipath at low cost is of value. Our method yields the least-squares estimation of joint TOA and AOA with low computational cost. It is based on the spectral observation of beam forming, in which the path overlapping effect is mitigated using multipath-aided acquisition. The computational cost is reduced using in-band power spectrum and accurate initial estimations. The performance is verified both in IEEE 802.15.4a CM3 channel model and in a real environment. Simulation results in CM3 channel model show that the TOA and AOA estimation improvements on average are 2.4cm and 13.1° in the dense multipath scenario. Measurement in an indoor open hall environment shows that the AOA error decreases from 10.6° to 7.2°, and the TOA error decreases from 2.1cm to 1.9cm when the path overlapping effects are mitigated in the range of 21m

Compact UWB bandpass filter with high suppression at 2.4 and 5.8 GHz

A circuit model is proposed for the design of an ultra-wideband (UWB) bandpass filter (BPF) with high out-of-band suppression at two different frequencies. Based on theoretical analysis and numerical simulation of this proposed circuit model, an UWB BPF is fabricated and measured for verification. This fabricated filter has a measured 3 dB passband of 3–4.5 GHz, with a compact size of only 10 × 9.8 mm. Moreover, it has a high rejection of 40 dB at 2.4 GHz, and 30 dB at 5.8 GHz, respectively. This UWB BPF is useful to alleviate the strong WLAN signals interference to UWB receivers

A novel E-DTDOA based one-way ranging using UWB-IR with unsynchronized anchors

In this article, a novel analytical equation is proposed to determine the equivalent time of arrival (E-TOA) for achieving sub-ns resolution, with much reduced analog-to-digital converter sampling frequency (in the order of 2-3 MHz). The timing information is extracted from high resolution channel impulse response, which is obtained using an equivalent time sampling (ETS) technique. The proposed E-TOA equation is different from the conventional real-time sampling equation due to the presence of an additional transmitter clock drift, and thus sensitive to both the transmitter and receiver clock drift variations. The validation of the E-TOA equation is carried out numerically using simulations along with experimental validation. The effect of timing uncertainties relating to the transmitter clock start time and the receiver clock offset is analyzed with variations in the transmitter and receiver clock drifts. With E-TOA measurements, an equivalent differential time difference of arrival based one-way ranging scheme for unsynchronized anchors is further proposed. It is thus demonstrated, using in house designed sensor nodes, that high ranging accuracy, in the order of few centimeters, can be achieved by utilizing the proposed analytical E-TOA technique, even with low sampling rate

5.8-GHZ suppressed UWB bandpass filter employing modified CRLH-TL of two and three unit cells

This paper presents a novel modified composite right/left-handed (CRLH) unit cell to achieve sharp rejection at 5.8 GHz. Design formulas are theoretically derived and numerically verified. Based on this unit cell, ultra-wideband (UWB) bandpass filters with two and three cells are designed, fabricated, and on-wafer measured. The measurement results show that the CRLH bandpass filter has a rejection of >60 dB at 5.8 GHz, a minimum insertion loss of 1.1 dB, and 3-dB bandwidths of 3.09-4.79 GHz and 3.22-4.61 GHz for the two and three unit cells, respectively.Published versio

A two-port antenna for wireless-powered UWB-RFID tags

This paper presents a two-port antenna including a receiving port and a transmitting one in the same volume. These two antennas are physically integrated and electrically isolated. The receiving antenna is a linearly polarized narrowband slot for energy harvesting, whereas the transmitting one is a circularly-polarized ultrawideband (UWB) quasi-spiral for signal radiation. The measurement results show that, the slot resonates at 5.8 GHz, and the quasi-spiral has a 10-dB return loss bandwidth of 2.85-5.16 GHz and a 3-dB axial ratio bandwidth of 3.05-4.43 GHz. The electrical isolation between these two antennas is more than 20 dB covering 1-8 GHz. This two-port antenna is a good candidate for wireless-powered UWB-RFID tags.Published versio

E-DTDOA based localization for wireless sensor networks with clock drift compensation

A high time resolution localization scheme, using ultra-wide band ranging signal with bandwidth of 2GHz, is proposed for a fully asynchronous wireless sensor network (WSN). The proposed scheme is specifically useful for sensor nodes which are designed to operate at very low ADC sampling rate, in the order of 2-3 MHz, but still achieves the sampling resolution in the order of sub-nanoseconds. To achieve low sampling rate, equivalent time sampling (ETS) technique is used at the sensor nodes. Reconstructed signal obtained by ETS technique, that require periodic transmission of the same signal repetitively, is severely affected by the variation in transmitter and receiver clock drift as against the real time sampling where the variations are due to receiver node clock drift only. Thus, it requires a protocol to precisely estimate the transmitter and receiver clock parameters. A scheme, which uses a novel mathematical equivalent time of arrival (E-TOA) model for ETS based system, for clock drift estimation is presented. Based on clock drift estimation parameters, receiver nodes are tuned to the same frequency. E-TOA measurements are further used to propose an equivalent differential time difference of arrival (E-DTDOA) based ranging algorithm, which relaxed the time synchronization requirement between the wireless nodes, and still achieving high time resolution. The E-DTDOA range measurements are subsequently used to obtain precise localization of the target node/s. The feasibility of the algorithm proposed is demonstrated experimentally using in house designed wireless sensor nodes

TOA estimation of UWB backscattering RFID tag with dual pulse modulation for clutter suppression

To realize precise localization for UWB backscattering RFID system, the arrival time of the direct path in the received signal (referred as time of arrival (TOA)) needs to be accurately estimated. The background clutter is one of the major factors that deteriorates the TOA estimation accuracy in backscattering RFID system. To suppress the background clutter while maintain low-complexity system design, we propose a novel UWB backscattering RFID system with its tag being implemented with dual pulse (DP) modulation. By transforming the mathematical model of received signal into a proper form, we discover the tag's sequence selection criteria which are able to mitigate the background clutter. For the proposed tag coded with dedicated sequences, a two-stage TOA estimation algorithm able to effectively mitigate clutter is developed. Simulation results show that the proposed RFID system coupled with the algorithm is able to achieve accurate TOA estimation in the environment where the clutter overwhelms the tag response

A brief review of wideband circularly-polarized planar antenna design

Wideband circularly-polarized antenna is one of the key components in the wireless systems. This paper briefly reviews the design mechanisms of circularly-polarized antenna, and discusses their advantages and disadvantages. In addition, two circularly-polarized planar antennas for ultra-wideband systems developed in our group are also presented and discussed in this paper

Development of a local area microwave network

77 p.An introduction to the background and approach taken in the project is given in chapter 1. This is followed by a detailed description of wireless network hardware in chapter 2. The wireless transceiver uses DPSK modulation on Manchester Encoded data. The transmission from users to a control station is in the form of burst frames of data in its original Ethernet form. Carrier frequencies of 1.88 GHz and 1.95 GHz are used to carry data from users to the control and in the reverse path in a full duplex operation manner. Multiple access protocol used is similar to CSMA/CD. The transmitter has a maximum EIRP of around 0 dBm. The receiver consists of a single stage down conversion to 70 MHz with incoherent DPSK demodulation at 70 MHz. The noise figure is 6.5 dB and the total power gain is 76 dB. The equivalent noise bandwidth is 71 MHz.RP 35/8