Base-station-assisted terminal-to-terminal connection setup

Details Base-station-assisted terminal-to-terminal connection setup Base-station-assisted terminal-to-terminal connection setup

1999-06-25

2003-06-03

Liu, Shuwang (Department: 2734)

Pulse or digital communications

Spread spectrum

Frequency hopping

C375S219000, C375S356000, C370S349000, C455S434000, C455S464000

Reexamination Certificate

active

06574266

ABSTRACT:

BACKGROUND
This invention relates to radio communication systems. In particular, it relates to ad-hoc radio systems that use frequency hopping in cordless telephony scenarios, such as cellular radio telephony and wireless local area networks (WLANs).
In the last decades, progress in radio and integrated circuits using very large scale integration (VLSI) technology has fostered widespread use of radio communications in consumer applications. Portable communication devices, such as mobile telephones, can now be produced having widely acceptable cost, size, and power consumption. Computing devices have experienced the same progress, leading from the desktop personal computer (PC) to notebook computers to sub-notebook computers and to personal digital assistants (PDAs). Today's miniaturized radio systems enable such computing devices to communicate wirelessly, either by themselves or in combination with mobile radio telephones. The separation between the telecommunication industry on the one hand and the PC industry on the other hand is gradually vanishing.
Many commercial wireless communication systems use the radio spectrum ranging from about 800 MHz up to about 5000 MHz (5 GHz). The radio spectrum is a scarce resource, and with the increasing need for that resource due to both the demand for increased bandwidth (higher data rates) and the continuously rising number of users, efficient spectrum usage is essential if the increasing need is to be met. This holds both for the spectrum controlled by communication system operators (licensed bands used for example for public radio telephony) and the spectrum that is free for all to use (unlicensed bands like the globally available industrial, scientific, and medical (ISM) bands at 900 MHz, 2400 MHz, and 5700 MHz).
Most radio systems in consumer applications today, like cellular or cordless telephony, wireless Internet, etc., consist of a fixed, wired infrastructure and portable terminals. The portable devices reach the infrastructure via access points or base stations. To be spectrally efficient, the radio spectrum is re-used in different geographical locations of the infrastructure. This means that independent users can use the same radio channel, provided their geographical separation is such that their signal-to-interference ratios, where the interference is co-channel interference, are good enough for acceptable reception. The current kind of interaction between wireless remote terminals and fixed infrastructures is acceptable since most communication takes place between wireless terminals and devices wired to the infrastructure (like a desk telephone, a computer server, a PC connected via a cable modem, etc.). However, wireless user scenarios are changing, and with the increasing proliferation of cheap radio transceivers, communication between portable devices will continue to increase. In particular, local (short-range) communication sessions between devices like laptop computers, printers, mobile phones etc., will increase in the coming years.
The current architecture of a wireless system like a cellular radio telephone system has a fixed part comprising a plurality of geographically separated base stations and a number of remote terminals, many of which may be portable.
FIG. 1
depicts the typical architecture of a radio system
100
, comprising fixed base stations (BS)
110
, which have respective radio coverage areas (cells)
120
indicated by the dashed lines, and portable terminals
140
. Each BS
110
typically has one or more radio transceivers that provide interfaces between the public switched telephone network and portable radio telephones and other remote terminals located in its cell. The fixed site transceivers
110
and remote terminals
140
communicate by exchanging RF signals, employing various formats (analog, digital, and hybrids) and access techniques (frequency division multiple access (FDMA), time division multiple access (TDMA), code division multiple access (CDMA), and hybrids). General aspects of such cellular radio telephone systems are known in the art.
Each BS
110
handles a plurality of traffic channels, which may carry voice, facsimile, video, and other information, through a traffic channel transceiver that is controlled by a control and processing unit. Also, each BS includes a control channel transceiver, which may be capable of handling more than one control channel and is also controlled by the control and processing unit. The control channel transceiver broadcasts control information over the control channel of the BS or cell to terminals
140
that are “locked”, or synchronized to that control channel. This locking allows the terminals
140
to be reached quickly and to reduce their power consumption since they are synchronized to the base stations.
In an FDMA radio telephone system, each remote terminal is allocated a radio channel (e.g., an RF carrier signal for transmitting and an RF carrier signal for receiving) for the duration of a communication session with the fixed site transceiver(s). The transmitters in the remote terminal and in the fixed site typically produce RF power levels that are controlled in a way that minimizes interference with other transmitters in the system.
In a TDMA radio telephone system like the Global System for Mobile communications (GSM) currently in use in many parts of the world, each carrier signal is time-shared by up to eight radio telephones, i.e., each carrier signal transports successive frames of eight time slots each. During its assigned time slot, a radio telephone tunes its transmitter to the proper frequency, ramps to the output power level, transmits the desired information, and then ramps down so as not to interfere with other users. In a GSM system, the length of each time slot is about 577 microseconds.
In a typical direct sequence CDMA (DS-CDMA) system, an information bit stream to be transmitted is superimposed on a much-higher-rate bit stream that typically consists of consecutive symbols that are sometimes called spreading sequences. Usually, each information bit stream is allocated a unique spreading sequence that is consecutively repeated to form the much-higher-rate bit stream. Each bit of the information bit stream and the spreading sequence are typically combined by multiplication, or modulo-2 addition, in a process sometimes called coding or spreading the information signal. The combined bits stream may be scrambled by multiplication by another, usually pseudo-noise, bit stream, with the result transmitted as a modulation of a carrier wave. A receiver demodulates the modulated carrier and correlates the resulting signal with the scrambling bit stream and the unique spreading sequence to recover the information bit stream that was transmitted.
In North America, a digital cellular radiotelephone system using TDMA is called the digital advanced mobile phone service (D-AMPS), some of the characteristics of which are specified in the TIA/EIA/IS-136 standard published by the Telecommunications Industry Association and Electronic Industries Association (TIA/EIA). Another digital communication system using direct-sequence CDMA is specified by the TIA/EIA/IS-95 standard, and a frequency-hopping CDMA communication system is specified by the EIA SP 3389 standard (PCS 1900). The PCS 1900 standard is an implementation of GSM for personal communication services (PCS) systems. In these communication systems, communication channels are implemented by frequency-modulating RF carrier signals that have frequencies near 800 megahertz (MHz), 900 MHz, 1800 MHz, and/or 1900 MHz. One form of GSM radio telephone communicates with an associated base station in the frequency bands 890-915 MHz (up link) and 935-960 MHz (down link), with each frequency band being divided into 124 channels with a separation of 200 KHz.
Communication between portable terminals is possible in these systems, of course, but today this is always mediated by one or more base stations
110
. For example, if both terminals are locked to the same base station, that base station es

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