Narrow beamwidth communication link with alignment camera

Details Narrow beamwidth communication link with alignment camera Narrow beamwidth communication link with alignment camera

2002-01-11

2003-07-01

Nguyen, Lee (Department: 2683)

Telecommunications

Transmitter and receiver at same station

Radiotelephone equipment detail

C455S424000, C455S025000, C455S067150, C455S067700, C343S894000, C343S874000, C343S754000, C343S720000, C342S359000

Reexamination Certificate

active

06587699

ABSTRACT:

BACKGROUND OF THE INVENTION
Wireless Communication Point-to-Point and Point-to-Multi-Point
Wireless communications links, using portions of the electromagnetic spectrum, are well known. Most such 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. Mobile telephone systems that have recently become very popular 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.
Need for High Volume Information Transmission
The need for faster (i.e., higher volume per unit time) information transmission is growing rapidly. Today and into the foreseeable future transmission of information is and will be 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 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 modem 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 T
1
links (each at 1.544 Mbps). Recently, microwave systems operation in the 11 to 38 GHz band have reportedly 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 vs. Frequency
Bandwidth-efficient modulation schemes allow, as a general rule, transmission of data at rates of 1 to 10 bits 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 hardwired 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.
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 attenuation of electromagnetic radiation increases generally with frequency in the microwave and millimeter-wave bands. However, excitation of rotational transitions in oxygen and water vapor molecules absorbs radiation preferentially in bands near 60 and 118 GHz (oxygen) and near 23 and 183 GHz (water vapor). Rain, which attenuates through large-angle scattering, increases monotonically with frequency from 3 to nearly 200 GHz. At the higher, millimeter-wave frequencies, (i.e., 30 GHz to 300 GHz corresponding to wavelengths of 1.0 millimeter to 1.0 centimeter) where available bandwidth is highest, rain attenuation in very bad weather limits reliable wireless link performance to distances of 1 mile or less. At microwave frequencies near and below 10 GHz, link distances to 10 miles can be achieved even in heavy rain with high reliability, but the available bandwidth is much lower.
Need For Special Alignment Methods And Apparatus
High frequency, large antennas are typically designed to produce very narrow beams which must be very accurately aligned. Because of the narrow beams, both transmit and receive antennas must be precisely pointed at each other. Gimbals for these antennas are typically designed with two pointing angles; therefore, the process of aligning two antennas is essentially a 4 dimensional search. Since the antennas of the instant invention (such as a four-foot diameter antenna) can have narrow beams in the range of 0.15 degrees or less and are capable of thousands of discrete positions in each dimension, there are an extremely large number of four-dimensional alignments over which to search. As will be shown below, a complete search of this four-dimensional space could theoretically consume many years.
Therefore, what is needed are equipment and methods for aligning a wireless data link having very narrow beam widths and keeping them aligned.
SUMMARY OF THE INVENTION
The present invention provides equipment and methods for aligning the antennas of a point-to-point wireless millimeter wave communications link and keeping them aligned. Each of two communicating antennas is equipped with a telescopic camera connected to a processor programmed to recognize landscape images. The processors are programmed to remember the pattern of the landscape as it appears when the antennas are aligned. Each of the cameras then view the landscape periodically or continuously and if the landscape in view changes by more than a predetermined amount a signal is provided to indicate a misalignment. An operator can then take corrective action or alternatively the antenna system can be configured for remote or automatic realignment based of feedback from the camera. In a preferred embodiment, the antennas are initially aligned by substituting a narrow band oscillator power source for the signal transmitting electronics associated with a first antenna and a power detector is substituted for the signal receiving electronics of associated with a second antenna. In preferred embodiments after a first alignment procedure is performed, the procedure is repeated with an oscillator power source connected to the

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