Search

This paper presents an analysis of the swept time delay crosscorrelator, as used in wideband, RF, channel sounding systems, with a view to examining its use in already occupied channels. It is shown that the probe signal can be selectively filtered at the transmitter and receiver to minimise interference to users within the band. This filtering degrades the dynamic range of the sounder and hence the dynamic range can be traded against the spatial resolution performance in a given scenario. An analysis of the various factors is presented and some sample results are discussed.

This paper investigates the channel parameters (time dispersive properties) for the novel idea of tiny communicators called 'specks'. These tiny devices are limited with power so a clear idea of the channel impairment is mandatory for the design of onboard DSP. In order to facilitate the design, measurement of the impulse response characteristic has been investigated through different media and antennas. The paper investigates the measured impulse response and statistical properties of amplitude variations for individual impulses for distances of around 10 cm in addition to power delay profile, path loss, mean excess delay, root mean square delay, coherence bandwidth, and their impact on system design. The narrowband model has been used to predict the path loss of the channel and extent of coverage of the transmitting speck. The wide band channel sounding has been done to investigate the impulse response parameters such as delay spread, which is used to compute several secondary statistics like coherence bandwidth and data rate. (8 pages)

The high latitude ionosphere is a dynamic region that is subject to a variety of disturbed conditions, which affect the propagation of HF radio signals. Point-to-point digital communication systems at high latitudes attempting to utilise the narrowband HF ionospheric radio channel can suffer severe performance degradation when the time or Doppler dispersion exceeds certain, system dependent, bounds. The presented results are based around measurements of narrowband pulse compression channel sounding signals, made using a six channel spaced array receiving system, over two high latitude paths. Super resolution direction finding studies of this data revealed significant directional effects in the received signals. Of particular note is an often observed directional structure to received Doppler spread signals. These investigations indicate that spatial filtering, using simple arrays of antennas, can significantly reduce the level of Doppler spread presented at the inputs to modern high speed digital modems. The use of fast solver methods to find the best spatial filtering solutions results in very similar performance at reducing Doppler spread and massively reduced calculation times, thus raising the possibility of implementation of spatial filtering in a real system.

1 ABSTRACT UMTS radio network planning differs from that of the 2nd Generation networks in many respects. As a CDMA air interface with multiple Spreading Factor, Forward Error Correction and Code Puncturing operating points, it is no longer sufficient to infer service performance via static signal strength predictions. In particular, as power is the resource shared on both uplink and downlink, a simulation-based approach must be adopted more closely to estimate the users' perceived Quality of Service. Previous work at the University of Bristol (Vernon, 1) has proposed a web-enabled distributed approach to UMTS radio network planning. Software written in the Java programming language is run on multiple web browsers; users requiring network planning resources can run simulations using surplus processing power on other users' workstations, accessed remotely over the Internet. Intermediate results presented in other fora have demonstrated the software's ability to simulate a number of controlled, plane-earth scenarios (Vernon et al., 2). This paper demonstrates how the planning tool was set up to simulate a real-world scenario. Using vector channel sounding data obtained from a MeDaV transmit-receive assembly interfaced to an Allgon-provided eight element array antenna, scatterer angle-delay-intensity plots were obtained for a number of test locations in Bristol City Centre. The experimental technique is analysed in more detail in Allan et al, 3, and is summarised in Figures 1 and 2. Using the data obtained from combining a number of plots, the propagation characteristics between source, scatterers and receiver for the area under test may be obtained. Calibration of the planning tool for areal density of scatterers and power coupling into and out of scattering centres can then be performed.

Smart antennas promise to provide range extension and capacity enhancements crucial to the successful deployment of Universal Mobile Telecommunications System (UMTS) networks. The frequency offset between the uplink and downlink in the frequency division duplex (FDD) air interface gives rise to a frequency dependency in the channel responses and potential problems in downlink beamforming. In order to investigate this, a highly novel dual-band, dual-polarised channel sounding trial was performed in the UMTS FDD bands by the University of Bristol. The wideband measurements were conducted in the City of Bristol, encompassing urban city and sub-urban residential scenarios and subsequent post processing was performed to extract channel parameters across the two bands. This paper presents the results and analysis done for the single polarisation static measurements. It was observed that in most instances, there was a higher degree of scattering in the higher frequency band, resulting in larger angular spreads and delay spreads. The channels also exhibited a strong degree of de-correlation when viewed from the spatial and temporal domains.

The high latitude ionosphere is a disturbed region containing irregularities which may be regarded as providing a rough reflecting surface for obliquely propagating HF radio waves. Signals associated with each propagation mode may arrive at the receiver over a range of angles in both azimuth and in elevation. In addition, ionospheric movements at the reflection points impose Doppler shifts and Doppler spreads onto the signal. Various researchers have been engaged in an experimental programme of channel sounding over high latitude paths with the DAMSON pulse compression sounder (Davies and Cannon 1993). The system allows signal strength, time-of-flight, time dispersion due to multipath propagation and frequency dispersion Doppler spread and Doppler shift to be measured over point-to-point communications paths. All of these parameters are of great importance to the design and operation of HF communications equipment in the high latitude regions. It is suggested here that signals may be combined from two or more antennas in such a way as to, in effect, steer beam(s) or null(s) in the directional sensitivity pattern of the receiver antenna so as to exploit the directional diversity of the incident signals in order to reduce the delay and Doppler spreads. Such a technique is potentially important for increasing the data throughput of communications systems employing modern, high speed modems operating within the high latitude environment.

The current interest in the development of third generation cellular radio systems has focused attention on propagation channel issues. CDMA systems occupy wide bandwidths, which typically exceed the channel coherence bandwidth, leading to severe frequency selective distortion. Extensive channel sounding campaigns have been carried out, and much data gathered, from which statistics may be derived to characterise these channels. These statistics may then be employed within generalised channel simulation software in non-real time, or within hardware channel emulators in real time. In this paper we consider an alternative method where channel sounding data may be accepted by a system simulation tool, which then predicts the performance of a particular radio system configuration. Benefits of this approach include simplicity, as reduction of the channel data to statistical parameters is not required, and realism as the actual recorded data is utilised.

This paper details the design, simulation, implementation, and on-air testing of a prototype synchronous ALE system which has been developed at Harris Corporation. This ALE system utilizes extremely robust burst serial tone waveforms to perform all channel linking, frequency evaluation, and link termination functions. The prototype system has been used as a test-bed to both measure the robustness of the waveforms and to explore a number of different linking techniques. A number of linking techniques have been examined including a single channel 3-way link set up (LSU) as well as a number of different multi-channel techniques. The multi-channel techniques include calling on the next available frequency, calling on a specified frequency, calling on the best frequency (with implied channel sounding) and calling on the first frequency to provide a specified level of performance. The paper begins with a discussion of the advantages and disadvantages of synchronous ALE systems or networks. This is followed by an explanation on the methods utilized to generate the presented results, both software simulation and on-air testing. Next is a discussion of the burst serial tone waveform utilized by the prototype system, including simulated performance. This is followed by the presentation of a simple single frequency link-set-up (LSU) technique. Simulated and on-air performance data is presented for this technique. Next, the operation of the synchronous, multi-channel ALE system is presented, along with some on-air performance data. The paper concludes with a summation of the results.

Observations of the direction of arrival of a narrow band pulsed channel sounding signal propagated over a high latitude path have been made with a multichannel receiver system connected to a wide aperture antenna array. The signals received on each antenna were processed to provide a measure of the relative times of flight of the propagating modes and their associated Doppler spectra. In this way, the signal was split into complex amplitude components distinguished by the antenna position, time of flight and Doppler frequency. A direction finding algorithm was then applied to each of the signal components in turn in order to determine the directional characteristics of the received signal.

Observations of the direction of arrival of a narrow band pulsed channel sounding signal propagated over a high latitude path have been made with a multi-channel receiver system connected to a wide aperture antenna array. The signals received on each antenna were processed to provide a measure of the relative times of flight of the propagating modes and their associated Doppler spectra. In this way, the signal was split into complex amplitude components distinguished by antenna position, time of flight and Doppler frequency. A direction finding algorithm was then applied to each of the signal components in turn in order to determine the directional characteristics of the received signal.

An automatic system for HF radiocommunications is described. Measurements of channel stability are presented the result of which favour an automatic link set-up process according to a prediction calculation combined with passive channel analysis rather than with channel sounding. The automatic link maintenance procedure embedded in the packet radio data transmission protocol RSX.25 comprises the adaptation of frame length, frequency and bandwidth. Channel analysis during data transmission is done by the control of the repetition rate. Depending on the defined thresholds, the aforementioned adaptation of system parameters is initiated. The results of field trials over good, medium and poor channels and the accompanying system behaviour are presented. Only in the case of severe interference the throughput drops below the mean value of 1800 bit/s. A comparison by computer simulation was done between the RSX.25 protocol and the packet radio protocol, which shows that both protocols may be improved by implementing the other's benefits.