Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
2000-07-12
2002-12-24
Chin, Vivian (Department: 2682)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S550100, C455S069000, C455S279100
Reexamination Certificate
active
06498939
ABSTRACT:
This invention relates to wireless networks, in particular to wireless networks in enclosed environments such as, for example, a home or office.
With the growing use of computer systems such as PCs within office or working environments provision of suitable conduits for the necessary cabling, in particular network cables, has become increasingly difficult. Furthermore, working environments are often altered such as rearranging an open-plan office, or reorganising partitions in an environment having conventional offices. In production facilities the increasing reliance on information technology makes computer networks essential—yet, again, the cabling requirements pose significant difficulties.
With the rapid increase in the number of multimedia appliances (e.g. video equipment, home theatres, PCs, etc) being used in the home, there is also a growing requirement for a network for controlling and connecting such multimedia appliances which is not unsightly. Such networks need to be easy to install, easy to set up, easy to maintain and easy to use. The required network should link the above-described home, office or production appliances to each other and to wide area networks such as, for example, the Internet, video servers or other communications media, via a central server.
It has been proposed to use wireless communication media for such networks which offer advantages over wired systems in that they are easy to physically install and such systems are known for use in the control of television systems, communication of audio signals to remote speakers, communication between a PC and a printer, and the like.
In such a wireless network, individual apparatus are linked to each other and/or a central server system by wireless communications and each apparatus can typically transmit and receive wireless signals. Such a system may be termed a wireless LAN
However, there is a need to transmit digital data at every increasing data rates for multimedia information. The carrier frequencies required for such data rates are at least in the Gigahertz (GHz) range. At carrier frequencies in the Gigahertz range, communication systems suffer from the effects of reflections and attenuation from walls, windows and partitions, etc, typically found in work or home environments which can affect the Bit Error Rate (BER) performance of the system, thereby resulting in retransmission of data and an undesirable or even unacceptable reduction in data throughout. A source of poor BER performance at so-called medium carrier frequencies, i.e. in the range about 2 to 15 GHz, is that reflections manifest themselves as sources of multipath propagation that can result in inter-symbol interference at a receiving apparatus. Additionally, many applications involve compressed video or audio and it is preferable for the data to arrive at the receiver in the correct order to avoid excessive buffering and delays, and/or complex error correction algorithms and processing circuitry to compensate for any lost or corrupted data.
In the case of medium frequency systems (2 to 15 GHz carrier frequencies), multipath signals at the receiver give rise to inter-symbol interference in the demodulated data stream. To reduce the effect of such multipath propagation, the system must utilise complex echo cancellation or equalisation techniques. In this application, the steerable antenna can be used to amplify the gain of the primary signal whilst attenuating the multipath signals with nulls, thus simplifying the echo cancelling requirements. Alternatively, in the case of a CDMA system where one wishes to increase the signal received from multipath signals at the input to the RAKE receiver, the steerable antenna can be used to increase the strength of the signal received at the RAKE receiver.
At very high carrier frequencies, i.e. in the range about 15 to 60 GHz, the attenuation due to walls or partitions, etc, gives rise to significant received signal power level problems, where the transmitting apparatus and receiving apparatus are not in line of sight. If there is excessive BER, the system performance and overall quality of audio-visual degrades due to the need for retransmission of erroneous data. At such high frequencies, it may be possible to only detect a signal resulting from a reflection from a partition or wall.
For very high carrier frequencies, simulation results show that the amount of diffusion of power through partitions and doors, etc is low and is highly dependent upon the material and construction of partitions and the position of furniture, for example. In addition, small changes in the-environment affect the propagation of RF within the building. At these frequencies (15 to 60 GHz), a reasonable level of reflection from walls and/or internal or external objects (via doors, windows, and the like) in the environment can be anticipated as disclosed in publication “Predicted HIPERLAN coverage and outage performance at 5.2 and 17 GHz using indoor 3D Ray tracing techniques” A R Nix et al, Wireless Communications Journal 1996.
Experimental results published in the literature, i.e. “Investigation of the Effects of Antenna Directivity on Wireless Indoor Communication Systems at 60 GHz” by M R Williams et al, Proceedings of Workshop on Wireless Multimedia Communication Systems, Kings College, June 97, show that the bit error rate (BER) performance of a wireless communication system can be dramatically improved by the use of highly directional antennas. In theory, optimum performance can be achieved if the beams of both the transmitter and receiver are aligned on the line of sight and the angle of spread of the beams are minimised in order to reduce reflections and multipath propagation. It is apparent that, as the beams narrow, a concomitant accuracy of beam alignment must be maintained. Also, the narrower the beam, the more rapid the degradation in performance if the beam goes out of alignment.
In the majority of home and work environments, it is highly improbable that line of sight communication between all appliances can be achieved, especially to those appliances that are ergonomically located. In a practical situation, in order to provide communication at such high frequencies, reliance upon reflections within the building or via windows to and from external objects or diffusion or diffraction through and under partitions and doors would be required in addition to, or alternatively to, line of sight, where possible, to maximise the likelihood of obtaining signal power levels suitable for communication.
In order to reduce the problems with unwanted reflections and poor signal strength due to attenuation through walls or partitions, etc, it is desirable to provide antennas which are directional so that they transmit and receive in narrow directions only. Thus, by properly aligning the directional antennas, the transmission problems giving rise to poor BER may be mitigated.
Although it is possible to create a computer simulation of the effects of a building on the propagation of a radio signal and to define the optimum position of transmitting and receiving antennas, and their direction of propagation, it is an impractical solution since the environment (location of obstructions, number and location of equipment, etc) often changes. Such a wireless home or work network is difficult to set up and maintain without continual adjustment and therefore further computer simulation.
Such an approach relies upon complex simulation of the transmission characteristics of the environment taking into account an accurate geometric map of the environment, the physical properties of materials comprising partitions and the effect of reflections from objects that are exterior of the building (reference “A Ray Tracing for Microcellular Wideband Propagation Modelling”, G E Athanasiadou et al, IEEE, VTC, Chicago, 1995). Any modification to the environment leads to either a requirement for a new simulation and repositioning of antennas or the possible degradation of the performance of the network.
In accordance with a first aspect of the pr
Brady W. James
Chin Vivian
Kempler William B.
Lee John J
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