Very high-speed digital RF clipper/modulator

Details Very high-speed digital RF clipper/modulator Very high-speed digital RF clipper/modulator

2002-12-17

2004-08-24

Chin, Stephen (Department: 2634)

Pulse or digital communications

Systems using alternating or pulsating current

Amplitude modulation

C375S300000

Reexamination Certificate

active

06782057

ABSTRACT:

FIELD OF THE INVENTION
This invention relates, generally, to methods for wireless transmission of data, and more specifically, to a carrier modulation method and system by which a radio frequency carrier, expressed, as a square wave can be amplitude modulated with maximum efficiency and speed with minimum phase delay and distortion. RF filtering is used to reduce the modulated square wave to its base band sine wave component after modulation. This modulation method and system may be used to modulate the carrier (clock) at any frequency up to and beyond the carrier frequency itself. This is useful in the implementation of broadband wireless systems.
BACKGROUND OF THE INVENTION
Radio transmission of information traditionally involves employing electromagnetic waves or radio waves as a carrier. Where the carrier is transmitted as a sequence of fully duplicated wave cycles or wavelets, no information is considered to be transmissible. To convey information, historically, the carrier has superimposed on it a sequence of changes that can be detected at a receiving point or station. The changes imposed correspond with the information to be transmitted, and are known in the art as “modulation”.
Where the amplitude of the carrier is changed in accordance with information to be conveyed, the carrier is said to be amplitude modulated (AM). Similarly, where the frequency of the carrier is changed in accordance with information to be conveyed, either rarified or compressed wave cycles are developed, and the carrier is said to be frequency modulated (FM), or in some applications, it is considered to be phase modulated. Where the carrier is altered by interruption corresponding with information, it is said to be pulse modulated.
Currently, essentially all forms of the radio transmission of information are carried out with amplitude modulation, frequency modulation, pulse modulation or combinations of one or more. All such forms of modulation have inherent inefficiencies. For instance, a one KHz audio AM modulation of a Radio Frequency (RF) carrier operating at one MHz will have a carrier utilization ratio of only 1:1000. A similar carrier utilization occurs with corresponding FM modulation. Also, for all forms of currently employed carrier modulation, frequencies higher and lower than the frequency of the RF carrier are produced. Since they are distributed over a finite portion of the spectrum on each side of the carrier frequency, they are called side frequencies and are referred to collectively as sidebands. These sidebands contain all the message information and it has been considered that without them, no message can be transmitted. Sidebands, in effect, represent a distribution of power or energy from the carrier and their necessary development has lead to the allocation of frequencies in terms of bandwidths by governmental entities in allocating user permits within the radio spectrum. This necessarily limits the number of potential users for a given RF range of the spectrum.
To solve the bandwidth crisis in the RF Spectrum, multiple access systems were developed. Multiple Access Systems are useful when more than one user tries to transmit information over the same medium. The use of multiple access systems is more pronounced in Cellular telephony; however, they are also used in data transmission and TV transmission. There are three common multiple access systems. They are as follows:
1—Frequency Division Multiple Access (FDMA)
2—Time Division Multiple Access (TDMA)
3—Code Division Multiple Access (CDMA)
FDMA is used for standard analog cellular systems. Each user is assigned a discrete slice of the RF spectrum. FDMA permits only one user per channel since it allows the user to use the channel 100% of the time. FDMA is used in the current Analog Mobile Phone System (AMPS).
In a TDMA system the users are still assigned a discrete slice of RF spectrum, but multiple users now share that RF carrier on a time slot basis. A user is assigned a particular time slot in a carrier and can only send or receive information at those times. This is true whether or not the other time slots are being used. Information flow is not continuous for any user, but rather is sent and received in “bursts”. The bursts are re-assembled to provide continuous information. Because the process is fast, TDMA is used in IS-54 Digital Cellular Standard and in Global Satellite Mobile Communication (GSM) in Europe. In large systems, the assignments to the time/frequency slots cannot be unique. Slots must be reused to cover large service areas.
CDMA is the basis of the IS-95 digital cellular standard. CDMA does not break up the signal into time or frequency slots. Each user in CDMA is assigned a Pseudo-Noise (PN) code to modulate transmitted data. The PN code is a long random string of ones and zeros. Because the codes are nearly random there is very little correlation between different codes. The distinct codes can be transmitted over the same time and same frequencies, and signals can be decoded at the receiver by correlating the received signal with each PN code.
The great attraction of CDMA technology from the beginning has been the promise of extraordinary capacity increases over narrowband multiple access wireless technology. The problem with CDMA is that the power that the mobiles are required to transmit goes to infinity as the capacity peak is reached. i.e. the mobiles will be asked to transmit more than their capacity allows. The practical consequence of this is that the system load should really be controlled so that the planned service area never experiences coverage failure because of this phenomenon. Thus CDMA is a tradeoff between maximum capacity and maximum coverage.
Over the previous few decades, electronically derived information has taken the form of binary formatted data streams. These data streams are, for the most part, transmitted through telecommunication systems, i.e., wire. Binary industry communication in general commenced with the networking of computer facilities in the mid 1960s. An early networking architecture was referred to as “Arpanet”. A short time later, Telenet, the first public packet-switched network, was introduced to commerce. As these networks grew, protocols for their use developed. For example, a coding protocol, ASCII (American Standard Code for Information Interchange) was introduced in 1964. Next, Local Area Networks (LAN) proliferated during the 1970s, the oldest and most prominent, Ethernet, having been developed by Metcalfe in 1973. Under the Ethernet concept, each station of a local system connects by cable to a transceiver and these transceivers are then inter-linked. In 1983, the Institute of Electrical and Electronic Engineers (IEEE) promulgated Ethernet with some modifications, as the first standard protocol for Local Area Networks. The Ethernet protocol remains a standard for essentially all forms of database conveyance or exchange.
While binary data stream transmission by wire has improved substantially in terms of data transfer rates, that improvement has not been the case where transmission is by utilization of the RF spectrum. Current technology in data stream transmission by wire is shown in U.S. Pat. No. 5,661,373 titled Binary digital signal transmission system using binary digital signal of electrically discharged pulse and method for transmitting binary digital signal and issued Aug. 26, 1997 to Nishizawa, which discloses a binary digital signal transmission system wherein a transmitter generates a binary digital signal including at least a rise portion where a level of the binary digital signal steeply rises in accordance with inputted binary digital data of a first value, and at least a fall portion where the level of the binary digital signal steeply falls in accordance with the inputted binary digital data of a second value, and then transmits the binary digital signal via a cable to a receiver. On the other hand, the receiver receives the transmitted binary digital signal, and first and second resonance circuits respectively have two resonance frequen

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