Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
2000-09-22
2004-10-12
Appiah, Charles (Department: 2686)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S517000, C455S343200, C455S127500, C713S323000, C370S311000, C340S007380
Reexamination Certificate
active
06804542
ABSTRACT:
BACKGROUND
The present invention relates to electronic communication systems and, more particularly, to sleep modes in asynchronous data communication schemes.
In the last decades, progress in radio and VLSI technology has fostered widespread use of radio communications in consumer applications. Mobile radios and other portable devices are common consumer devices.
Presently, the primary focus of wireless communication technology is on voice communication. This focus will likely expand in the near future to provide inexpensive radio equipment which can be easily integrated into mobile and stationary devices. For instance, radio communication can be used to create wireless data links and thereby reduce the number of cables used to connect electronic devices. Recently, a new radio interface called Bluetooth was introduced to replace the cables used to connect laptop computers, headsets, PDAs, and other electronic devices. Some of the implementation details of Bluetooth are disclosed in this application, while a detailed description of the Bluetooth system can be found in “BLUETOOTH—The universal radio interface for ad hoc, wireless connectivity,” by J. C. Haartsen, Ericsson Review No. 3, 1998.
Radio communication systems for personal use differ significantly from radio systems like the public mobile phone network. Public mobile phone networks use a licensed band which is fully controlled by the network provider and guarantee a substantially interference-free channel.
In contrast, personal radio communication equipment operates in an unlicensed spectral band and must contend with uncontrolled interference. One such band is the globally-available ISM (Industrial, Scientific, and Medical) band at 2.45 GHz. The band provides 83.5 MHz of radio spectrum. Since the ISM band is open to anyone, radio systems operating in this band must cope with several unpredictable sources of interference, such as baby monitors, garage door openers, cordless phones, and microwave ovens. Interference can be avoided using an adaptive scheme that finds an unused part of the spectrum. Alternatively, interference can be suppressed by means of spectrum spreading. In the U.S., radios operating in the 2.45 GHz ISM band are required to apply spectrum-spreading techniques if their transmitted power levels exceed about 0 dBm.
Bluetooth radios use a frequency-hop/time-division-duplex (FH/TDD), spread spectrum access scheme. This radio technology supports low-cost, low-power implementations. Frequency-hop systems divide the frequency band into several hop channels. During a connection, radio transceivers hop from one channel to another in a pseudo-random fashion. The instantaneous (hop) bandwidth is small in frequency-hop radios, but spreading is usually obtained over the entire frequency band. This results in low-cost, narrowband transceivers with strong immunity to interference. Occasionally, interference jams a hop channel, causing faulty reception. When this occurs, error-correction schemes in the link can recover lost data.
The channel is divided into time slots, or intervals of 625 &mgr;s, wherein a different hop frequency is used for each slot. This results in a nominal hop rate of 1,600 hops per second. One packet can be transmitted per interval/slot. Subsequent slots are alternately used for transmitting and receiving, which results in a TDD scheme.
The channel makes use of several, equally spaced, 1 MHz hops. With Gaussian-shaped frequency shift keying (FSK) modulation, a symbol rate of 1 Mbit/s can be achieved. In countries where the open band is 80 MHz or broader, 79 hop carriers have been defined. On average, the frequency-hop sequence visits each carrier with equal probability.
Bluetooth radio communications are based on peer communications and ad-hoc networking. In peer communications, all units are equal and a hierarchical network with a fixed infrastructure of base stations and portable terminals is not required. There is no centralized control that provides resource and connection management and other support services. In ad-hoc networks, which are usually based on peer communications, any unit can establish a connection to any other unit within range.
One application for Bluetooth-enabled communication units is the replacement of cables that connect computing or communication devices, such as computers, printers, mobile terminals, and the like. For systems such as Bluetooth to replace cables, data traffic over the radio interface must be very flexible. The enabling protocol must support both symmetric and asymmetric traffic flows and synchronous and asynchronous clocking schemes. In Bluetooth, a flexible communication channel is achieved using a slot structure without an overriding multi-slot frame structure. Bluetooth divides the time domain into slots and Bluetooth-enabled units are free to allocate the slots as necessary for transmission or reception.
As in other mobile radio communication systems, one important issue in peer-to-peer and ad-hoc communications is power conservation in mobile terminals. Since the radio communication typically takes place between portable and mobile equipment, low power consumption is essential to preserve battery life.
In communication networks, like cellular networks, low power modes are supported by the control channels of the network base stations. Such power conservation schemes are described in U.S. Pat. No. 5,794,146 to Sevcik et al., U.S. Pat. No. 5,758,278 to Lansdowne, commonly-assigned U.S. Pat. No. 5,883,885 to Raith, and International Patent Publication No. WO 00/04738. The base stations are typically fixed and not subject to power limitations. Once the terminal is synchronized to the base station, the terminal can enter a very low power mode. While in a low power mode, the terminal periodically scans for a signal from the base station, with each scan lasting for a short period of time. The base station, which is not constrained by power limitations, can broadcast the control channel or beacon continuously. The terminal can reduce its standby power considerably without sacrificing response time. Similar techniques are used on cellular asynchronous data channels, such as General Packet Radio Service (GPRS), which uses a control channel to schedule packet deliveries. A method of power conservation in a battery-operated, portable device is also described in European Patent Publication No. EP 0 944 273 A1.
Ad-hoc radio communications schemes like Bluetooth lack a control channel concept. Reducing power consumption while the device is in idle mode (i.e., not connected) has been described in commonly assigned U.S. Pat. No. 5,940,431 entitled “Access Technique of Channel Hopping Communications System,” to J. C. Haartsen and P. W. Dent, the disclosure of which is incorporated here by reference. However, reducing power consumption while terminals are connected but during pauses between asynchronous data bursts presents technical problems that are not trivial, particularly when both units have to minimize power consumption.
Accordingly, there is a need in the art for a system and method to reduce power consumption in radio units engaged in asynchronous data services. More particularly, there is a need for a system and method that allows the radio units to enter a sleep mode without requiring extra overhead.
SUMMARY
In peer-to-peer radio communications supporting asynchronous services, it is desired to reduce the power consumption in mobile terminals during pauses between data bursts. When there is no traffic on the channel for a predetermined amount of time, the units enter a low duty cycle sleep mode in which they sleep most of the time and wake up periodically, with a period T, to scan the channel for a brief time. A unit can restart communications only at specific points in time which relate to the sleep period T. The scan cycle of one unit preferably corresponds to the restart cycle of the other unit. If, for several sleep cycles, traffic does not return, T can be increased. This process may be carried out in both units, but without the units communicating
Appiah Charles
Burns Doane Swecker & Mathis L.L.P.
Perez-Gutierrez Rafael
Telefonaktiebolaget LM Ericsson (publ)
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