Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
2001-09-14
2004-03-30
Banks-Harold, Marsha D. (Department: 2686)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S562100
Reexamination Certificate
active
06714800
ABSTRACT:
BACKGROUND OF THE INVENTION
Local Wireless Radio Communication
Local wireless communication services represent a very rapidly growing industry. These services include paging and cellular telephone services. The cellular telephone industry currently is in its second generation with several types of cellular telephone systems being promoted. The cellular market in the United States grew from about 2 million subscribers and $2 million in revenue in 1988 to more than 60 million subscribers about $30 billion in revenue in 1998 and the growth is continuing in the United States and also around the world as the services become more available and prices decrease.
FIG. 1
describes a typical cellular telephone system. A cellular service provider divides its territory up into hexagonal cells as shown in FIG.
1
. These cells may be about 5 miles across, although in densely populated regions with many users these cells may be broken up into much smaller cells called micro cells. This is done because cellular providers are allocated only a limited portion of the radio spectrum. For example, one spectral range allocated for cellular communication is the spectral range: 824 MHz to 901 MHz. (Another spectral range allocated to cellular service is 1.8 GHz to 1.9 GHz) A provider operating in the 824-901 MHz range may set up its system for the cellular stations to transmit in the 824 MHz to 851 MHz range and to receive in the 869 MHz to 901 MHz range. The transmitters both at the cellular stations and in devices used by subscribers operate at very low power (just a few Watts) so signals generated in a cell do not provide interference in any other cells beyond immediate adjacent cells. By breaking its allocated transmitting spectrum and receive spectrum in seven parts (A-G) with the hexagonal cell pattern, a service provider can set up its system so that there is a two-cell separation between the same frequencies for transmit or receive, as shown in
FIG. 1. A
one-cell separation can be provided by breaking the spectrum into three parts. Therefore, these three or seven spectral ranges can be used over and over again throughout the territory of the cellular service provider. In a typical cellular system each cell (with a transmit bandwidth and a receive bandwidth each at about 12 MHz wide) can handle as many as about 1200 two-way telephone communications within the cell simultaneously. With lower quality communication, up to about 9000 calls can be handled in the 12 MHz bandwidth. Several different techniques are widely used in the industry to divide up the spectrum within a given cell. These techniques include analog and digital transmission and several techniques for multiplexing the digital signals. These techniques are discussed at pages 313 to 316 in The Essential Guide to Telecommunications, Second Edition, published by Prentice Hall and many other sources. Third generation cellular communication systems promise substantial improvements with more efficient use of the communication spectra.
Other Prior Art Wireless Communication Techniques
Point-to-Point and Point-to-Multi-Point
Most wireless communication, at least in terms of data transmitted is one way, point to multi-point, which includes commercial radio and television. However, there are many examples of point-to-point wireless communication. Cellular telephone systems, discussed above, are examples of low-data-rate, point-to-point communication. Microwave transmitters on telephone system trunk lines are another example of prior art, point-to-point wireless communication at much higher data rates. The prior art includes a few examples of point-to-point laser communication at infrared and visible wavelengths.
Information Transmission
Analog techniques for transmission of information are still widely used; however, there has recently been extensive conversion to digital, and in the foreseeable future transmission of information will be mostly digital with volume measured in bits per second. To transmit a typical telephone conversation digitally utilizes about 5,000 bits per second (5 Kbits per second). Typical personal computer modems connected to the Internet operate at, for example, 56 Kbits per second. Music can be transmitted point to point in real time with good quality using MP3 technology at digital data rates of 64 Kbits per second. Video can be transmitted in real time at data rates of about 5 million bits per second (5 Mbits per second). Broadcast quality video is typically at 45 or 90 Mbps. Companies (such as line telephone, cellular telephone and cable companies) providing point-to-point communication services build trunk lines to serve as parts of communication links for their point-to-point customers. These trunk lines typically carry hundreds or thousands of messages simultaneously using multiplexing techniques. Thus, high volume trunk lines must be able to transmit in the gigabit (billion bits, Gbits, per second) range. Most modern trunk lines utilize fiber optic lines. A typical fiber optic line can carry about 2 to 10 Gbits per second and many separate fibers can be included in a trunk line so that fiber optic trunk lines can be designed and constructed to carry any volume of information desired virtually without limit. However, the construction of fiber optic trunk lines is expensive (sometimes very expensive) and the design and the construction of these lines can often take many months especially if the route is over private property or produces environmental controversy. Often the expected revenue from the potential users of a particular trunk line under consideration does not justify the cost of the fiber optic trunk line. Digital microwave communication has been available since the mid-1970's. Service in the 18-23 GHz radio spectrum is called “short-haul microwave” providing point-to-point service operating between 2 and 7 miles and supporting between four to eight T1 links (each at 1.544 Mbps). Recently, microwave systems operating in the 11 to 38 Ghz band have been designed to transmit at rates up to 155 Mbps (which is a standard transmit frequency known as “OC-3 Standard”) using high order modulation schemes.
Data Rate and Frequency
Bandwidth-efficient modulation schemes allow, as a general rule, transmission of data at rates of about 1 to 8 bits per second per Hz of available bandwidth in spectral ranges including radio wave lengths to microwave wavelengths. Data transmission requirements of 1 to tens of Gbps thus would require hundreds of MHz of available bandwidth for transmission. Equitable sharing of the frequency spectrum between radio, television, telephone, emergency services, military and other services typically limits specific frequency band allocations to about 10% fractional bandwidth (i.e., range of frequencies equal to about 10% of center frequency). AM radio, at almost 100% fractional bandwidth (550 to 1650 GHz) is an anomaly; FM radio, at 20% fractional bandwidth, is also atypical compared to more recent frequency allocations, which rarely exceed 10% fractional bandwidth.
Reliability Requirements
Reliability typically required for wireless data transmission is very high, consistent with that required for hard-wired links including fiber optics. Typical specifications for error rates are less than one bit in ten billion (10
−10
bit-error rates), and link availability of 99.999% (5 minutes of down time per year). This necessitates all-weather link operability, in fog and snow, and at rain rates up to 100 mm/hour in many areas. On the other hand cellular telephone systems do not require such high reliability. As a matter of fact cellular users (especially mobile users) are accustom to poor service in many regions.
Weather Conditions
In conjunction with the above availability requirements, weather-related attenuation limits the useful range of wireless data transmission at all wavelengths shorter than the very long radio waves. Typical ranges in a heavy rainstorm for optical links (i.e., laser communication links) are 100 meters, and for microwave links, 10,000 meters.
Atmospheric atten
Johnson Paul
Kolinko Vladimir
Lovberg John
Olsen Randall
Tang Kenneth Y.
Banks-Harold Marsha D.
Perez-Gutierrez Rafael
Ross John R.
Ross, III John R.
Trex Enterprises Corporation
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