Roelof Schiphorst

A (simplified) Bluetooth maximum a posteriori probability (MAP) receiver

In our software-defined radio project, we aim at combining two standards luetooth and HIPERLAN/2. The HIPERLAN/2 receiver requires more computational power than Bluetooth. We choose to use this computational power also for Bluetooth and look for more advanced demodulation algorithms such as a maximum a posteriori probability (MAP) receiver. The paper discusses a simplified MAP receiver for Bluetooth GFSK signals. Laurent decomposition provides an orthogonal vector space for the MAP receiver. As the first Laurent waveform contains the most energy, we have used only this waveform for our (simplified) MAP receiver. This receiver requires a E/sub b//N/sub 0/ of about 11 dB for a BER of 10/sup -3/, required by the Bluetooth standard. This value is about 6 dB better than single bit demodulators. This performance is only met if the receiver has exact knowledge of the modulation index.

Evaluation of Spectrum Occupancy in Amsterdam Using Mobile Monitoring Vehicles

Dynamic Spectrum Access (DSA) is an exciting new technology, which introduced a paradigm shift in spectrum access. As a result it also changes the role of the regulator. On one hand the scarce radio spectrum should be used in an optimal way, so that the society is best served. On the other hand interference between users and networks should be avoided. For that reason rules have to be defined for spectrum use, which are not only determined by technical parameters, also economical, legal, political and social constraints play an important role. This topic is called spectrum governance. For evaluation purposes a monitoring network is necessary, which is also supported by several papers, that argue the need for a monitoring network to assure compliance of (DSA) radio equipment with regulatory rules. Traditional networks of fixed monitoring sites are not qualified anymore, as modern communication use high frequencies, above the 800 MHz, and communicate mainly locally. In this paper, we propose to extent this monitoring network by a fleet of mobile monitoring vehicles.

Near Vertical Incidence Skywave Propagation: Elevation Angles and Optimum Antenna Height for Horizontal Dipole Antennas

Near Vertical Incidence Skywave (NVIS) communication uses the ionosphere as a reflector to cover a continuous area with a radius of at least 150 km around the transmitter, on frequencies typically between 3 and 10 MHz. In developing countries, in areas lacking any other telecommunication infrastructure, it is used on a daily basis for voice and data communication. It may also be used in ad-hoc emergency (disaster) communication in other regions. This paper proposes optimum heights above ground for horizontal dipole antennas for NVIS, based on simulations and empirical data. First, the relationship between elevation angle and skip distance is obtained using ionospheric ray tracing. The high elevation angles found by simulation are confirmed by elevation angle measurements using a professional radio direction finder. The measurements also show the dominance of NVIS over ground wave propagation starting at a short distance. For these elevation angles, the optimum receive and transmit antenna heights above ground are derived using antenna simulations. A distinction is made between optimum transmit signal strength and optimum received signal-to-noise ratio (SNR). These optima are verified experimentally, demonstrating a novel evaluation method that can be used in the presence of the fading typical for ionospheric propagation. For farmland soil ( 20 mS/m, r 17) the optimum height above ground for the transmit antenna is 0.180.22. If the antenna is lowered to 0.02 a transmit signal loss of 12 dB occurs. This corresponds with the theory. The receive antenna height, however, while appearing uncritical in the simulations, showed a clear optimum at 0.16 and a 27 dB SNR deterioration when lowered to 0.02.

Mixed-path trans-horizon UHF measurements for P.1546 propagation model verification

An extensive propagation measurement survey was performed between The Netherlands and the United Kingdom. Seven mixed land/sea paths were monitored simultaneously, with path lengths ranging from 55 to 370 km. Eight frequencies between 500 and 700 MHz were used. Over 21 million measurements were collected during 500 days. This paper describes the survey and actions taken to assure high data quality. Detailed results are provided and can be used as propagation model test vectors. These results are compared with predictions of the ITU-R Rec. P.1546-4 propagation model. The results are disappointing: differences of up to 20 dB are found. Suggestions are made for improvement of the model.

A Monitoring Network for Spectrum Governance

Dynamic Spectrum Access (DSA) is an exciting new technology, which has introduced a paradigm shift in spectrum access. As a result it also changes the role of the regulator. On one hand the scarce radio spectrum should be used in an optimal way, so that society is best served. On the other hand interference between users and between networks should be avoided. For that reason rules have to be defined for spectrum use. This topic is called spectrum governance. For evaluation and to check whether devices obey the rules, a monitoring system is needed. In this paper, we propose to use a fleet of mobile monitoring vehicles for this purpose.

Implementation alternatives for a flexible wireless LAN transceiver

In our software-defined radio project we have implemented two different types of standards, a continuous-phase-modulation (CPM) based standard, Bluetooth, and an OFDM based standard, HiperLAN/2, on a general-purpose processor. First we describe our baseband software-defined radio testbed for the physical layer of wireless LAN standards. All physical layer functions have been successfully mapped on a Pentium 4 processor that performs these functions in real-time. The testbed consists of a transmitter PC with a DAC board and a receiver PC with an ADC board. Channel selection functionality is performed at the DAC and ADC board, whereas all modulation and demodulation functions are mapped on software running on the CPU. Then, three implementation alternatives for the digital part of the transceiver are introduced. These include: n-the testbed: a PCI card equipped with analog frontend functionality. All demodulation functions are performed in software running on the CPU of the notebook. n- integration of analog front-end functionality in the chipset of the motherboard and demodulation functions are performed by the processor. n- a low power DSP plus analog front-end functionality mounted on a PCI card. nThe alternatives are evaluated with respect to computational-power requirements, power consumption and expected manufacturing costs.

On-demand receive filtering in an UMTS terminal

This paper describes a novel on-demand receive filter in an UMTS terminal. The receive filter is the first function after the Analog-to-Digital converter and is for that reason one of the most computation intensive parts in a receiver. The proposed filter architecture measures the out-of-band interference and calculates the required attenuation, which is used to select the appropriate filter. To assess the advantages of this on-demand receive filter, we have carried out field strength measurements in the UMTS FDD downlink band (2.1 GHz). These measurements were carried out in Amsterdam, a dense urban area with 5 active UMTS operators. Our measurement results show that in a live network configuration there is almost no out-of-band interference. Moreover, an on-demand filter would save in this case more than 68% power compared to a fixed conventional receive filter.

The effects of nonlinear power amplifiers on the performance of a HiperLAN/2 system

Real-world power amplifiers (PAs) are weakly nonlinear. The nonlinear behavior causes subcarrier intermodulation in OFDM based transmitters. This paper shows the results of simulations performed on a software HiperLAN/2 system with a nonlinear power amplifier model. We show that HiperLAN/2 is much less sensitive to nonlinearities of the PA when BPSK or QPSK modulated sub-carriers are used compared to QAM16 or QAM64 modulated sub-carriers. Both QAM16 and QAM64 require a PA backoff amount of at least 5 dB while BPSK and QPSK dont require any backoff. This means that BPSK or QPSK modulated OFDM is more power efficient.