Communications: directive radio wave systems and devices (e.g. – Directive – Including directive communication system
Reexamination Certificate
2001-05-10
2003-09-16
Blum, Theodore M. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including directive communication system
C342S368000, C342S374000, C455S278100
Reexamination Certificate
active
06621454
ABSTRACT:
BACKGROUND
Currently, there are several so-called “last mile” and “last foot” data transmission systems which are designed to deliver high speed and/or high data capacity from the internet backbone to the end user. Several such systems use RF transmission to replace copper wire or fiber optic cables. Some of these systems are called point to point or point to multipoint systems and operate in the various licensed and unlicensed RF bands. A fundamental characteristic of such existing systems is that their RF transmissions occur in a frequency spectrum protected and regulated by a government body. These protected frequency spectrums, or bands, are licensed to certain license holders and only a few may operate in any given physical area depending upon the number of licenses available.
When operating in a licensed band the interference between transmissions is primarily self-interference and is thus controllable. Accordingly, noise (interference from another transmitter on the same frequency or on an interfering frequency) originates from a known source.
License holders are afforded protection from interference that is not self-generated which occurs within their allocated frequency band. Thus, in a protected band, if an interferer is detected, the licensed user could notify the FCC (or other regulating agency) and request that the agency investigate and rectify the problem. The regulations in the unlicensed bands differ in that systems must be designed to operate in the presence of interference and, in addition, must not generate interference. There are strict usage guidelines for the unlicensed spectrum. If an operator's equipment in not able to tolerate interference from a system complying with the FCC guidelines, then the operator cannot appeal to the FCC to alleviate the problem.
In licensed bands, such as the cellular telephone bands; the wireless multichannel multipoint distribution service (MMDS) frequencies, which are also used for fixed wireless; or local multipoint distribution service (LMDS) used for fixed wireless; if an operator were to detect interference in the band that was not self interference, the recourse would be to contact the FCC in order to have the government identify that source of interference and have the offending provider reduce or remove that interference. These bands are licensed, have been paid for and are owned by a certain operator.
Another method for reducing interference in the licensed bands, for a cellular or fixed wireless system, is through frequency planning of the system. The only true interference of concern within these licensed bands is self-interference. So, the operator is responsible for creating a system that has acceptable levels of background interference. Traditionally, operators have mitigated interference through frequency planning, cell location and sectorization of antennas. However, use of more sophisticated techniques is generally not necessary.
There are only a limited number of licensed bands in any geographic area, thus, in order to widen the choices consumers have, it is desirable for service providers to be able to use unlicensed RF bands to provide capability to deliver high speed, high capacity data services. In addition, a service provider may not hold licenses in every geographic area that it desires to provide service. Therefore, use of the unlicensed frequency bands may allow a service provider to cover a greater area.
In 1997 the FCC created a wireless arena called Unlicensed National Information Infrastructure (U-NII). System operators are free to operate wireless equipment in three sub-bands (5.15 to 5.25 GHz, 5.25 to 5.35 GHz and 5.725 to 5.825 GHz) without acquiring a licensed frequency spectrum. Part 15 of the FCC document specifies the conditions for operating wireless equipment in the U-NII frequency band. However, operators are not protected from possible interference from other U-NII operators transmitting in the vicinity or even other systems which utilize the same frequencies.
The IEEE, a standards group, is defining a wireless LAN standard, referred to as IEEE 802.11a for operation in the U-NII band. Equipment that conforms to this standard will operate indoors at the lower and middle frequency sub-band i.e. 5.15 to 5.25 GHz and 5.25 to 5.35 GHz. The ETSI BRAN group in Europe has defined an air interface standard for high-speed wireless LAN equipment that may operate in the U-NII frequency band. Equipment that is compatible with this standard may cause interference with use of these unlicensed bands.
One major problem with the use of such unlicensed bands is that it is very difficult, if not impossible, to control RF interference from other users of the unlicensed band. These other users may be using the selected unlicensed band for uses which are essentially different from that employed to deliver communication services. For example, the 5.25 to 5.35 GHz and 5.725 to 5.825 GHz bands are available for use for outdoor data communication between two points. This is typically a wideband use. The same bands are also available for other applications including users such as government radar. When the same band is used for wideband communication, and also used by others for uses such as radar, data communications between sending and receiving antennas will experience significant interference from radar pulses, which are broadcast over a wide area in repetitive bursts.
In the current state of the art, there is no discrimination between narrow band or wideband interference. When interference is detected, it is usually based on a signal to noise ratio for any given channel, then the radio switches to a lower order modulation, from either 64QAM to 16QAM, or 16QAM to QPSK, or QPSK to BPSK. Such a lower modulation shift allows more tolerance for noise and interference, but significantly reduces the data rate. Similarly, for Orthogonal Frequency Division Multiplexing (OFDM), the modulation order of the subcarriers is optimized for any given signal to noise ratio.
The prior art of radar interference mitigation is intended for use in currently licensed RF bands. However, radar interference is not an issue of great concern in licensed bands because there is little or no such interference. Most licensed bands are free and clear of other harmful interferers originating from outside sources. Additionally, most unlicensed bands do not have strong radar interferers. However, there is other low level interference in the unlicensed RF bands. This interference is at a much lower level and has a different signature than high powered radar. Therefore, generally speaking, prior art interference mitigation systems do not detect radar interference nor do they attempt to avoid it.
An important issue in unlicensed frequency band data transmission is the large amount of interference that can be present within the system. Interference is generated within the system, as well as coming from outside sources. Interference can come from other operators in the U-NII bands, point-to-point microwave links operating in the bands, or high powered radar systems. In order to deploy a system with high through-put using these bands, it is necessary to mitigate the interference caused by these different sources. The interferences of primary concern for the present invention are point-to-point microwave links and radar pulses, due to their high power. Microwave link power can be on the order of 10 to 20 dB higher power than the output allowed for unlicensed point to multipoint systems. Radar systems can also be significantly higher powered, and thereby a destructive interference source for an unlicensed data transmission system. The two different types of interference have different impacts on the design of a RF data transmission network.
Generally speaking, these interferences are somewhat unique to unlicensed bands. It is practically impossible to keep out and control unwanted frequencies in these bands. The bands are by definition unlicensed and therefore available to anyone to use as long as the equipment complies with the FCC rules gove
Prismantas Jerry
Reudink Mark D.
Rothaar Bruce C.
Blum Theodore M.
Fulbright & Jarworski L.L.P.
Vectrad Networks Corporation
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