Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1999-11-03
2003-10-07
Trost, William (Department: 2683)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S468000, C370S335000, C370S342000, C370S348000, C370S461000
Reexamination Certificate
active
06631124
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to communications methods and apparatus, and more particularly, to methods and apparatus for allocating resources in wireless communications.
Wireless communications systems are commonly employed to provide voice and data communications to subscribers. For example, analog cellular radiotelephone systems, such as those designated AMPS, ETACS, NMT-450, and NMT-900, have long been deployed successfully throughout the world. Digital cellular radiotelephone systems such as those conforming to the North American standard IS-54 and the European standard GSM have been in service since the early 1990's. More recently, a wide variety of wireless digital services broadly labeled as PCS (Personal Communications Services) have been introduced, including advanced digital cellular systems conforming to standards such as IS-136 and IS-95, lower-power systems such as DECT (Digital Enhanced Cordless Telephone) and data communications services such as CDPD (Cellular Digital Packet Data). These and other systems are described in
The Mobile Communications Handbook
, edited by Gibson and published by CRC Press (1996).
FIG. 1
illustrates a typical terrestrial cellular radiotelephone communication system
20
. The cellular radiotelephone system
20
may include one or more radiotelephones (mobile terminals)
22
, communicating with a plurality of cells
24
served by base stations
26
and a mobile telephone switching office (MTSO)
28
. Although only three cells
24
are shown in
FIG. 1
, a typical cellular network may include hundreds of cells, may include more than one MTSO, and may serve thousands of radiotelephones.
The cells
24
generally serve as nodes in the communication system
20
, from which links are established between radiotelephones
22
and the MTSO
28
, by way of the base stations
26
serving the cells
24
. Each cell
24
will have allocated to it one or more dedicated control channels and one or more traffic channels. A control channel is a dedicated channel used for transmitting cell identification and paging information. The traffic channels carry the voice and data information. Through the cellular network
20
, a duplex radio communication link may be effected between two mobile terminals
22
or between a mobile terminal
22
and a landline telephone user
32
through a public switched telephone network (PSTN)
34
. The function of a base station
26
is to handle radio communication between a cell
24
and mobile terminals
22
. In this capacity, a base station
26
functions as a relay station for data and voice signals.
As illustrated in
FIG. 2
, a satellite
42
may be employed to perform similar functions to those performed by a conventional terrestrial base station, for example, to serve areas in which population is sparsely distributed or which have rugged topography that tends to make conventional landline telephone or terrestrial cellular telephone infrastructure technically or economically impractical. A satellite radiotelephone system
40
typically includes one or more satellites
42
that serve as relays or transponders between one or more earth stations
44
and terminals
23
. The satellite conveys radiotelephone communications over duplex links
46
to terminals
23
and an earth station
44
. The earth station
44
may in turn be connected to a public switched telephone network
34
, allowing communications between satellite radiotelephones, and communications between satellite radio telephones and conventional terrestrial cellular radiotelephones or landline telephones. The satellite radiotelephone system
40
may utilize a single antenna beam covering the entire area served by the system, or, as shown, the satellite may be designed such that it produces multiple minimally-overlapping beams
48
, each serving distinct geographical coverage areas
50
in the system's service region. The coverage areas
50
serve a similar function to the cells
24
of the terrestrial cellular system
20
of FIG.
1
.
Several types of access techniques are conventionally used to provide wireless services to users of wireless systems such as those illustrated in
FIGS. 1 and 2
. Traditional analog cellular systems generally employ a system referred to as frequency division multiple access (FDMA) to create communications channels, wherein discrete frequency bands serve as channels over which cellular terminals communicate with cellular base stations. Typically, these bands are reused in geographically separated cells in order to increase system capacity.
Modem digital wireless systems typically utilize different multiple access techniques such as time division multiple access (TDMA) and code division multiple access (CDMA) to provide increased spectral efficiency. In TDMA systems, such as those conforming to the GSM or IS-136 standards, carrier frequencies are divided into sequential time slots that are assigned to multiple channels such that a plurality of channels may be multiplexed on a single carrier. CDMA systems, such as those conforming to the IS-95 standard, achieve increased channel capacity by using “spread spectrum” techniques wherein a channel is defined by modulating a data-modulated carrier signal by a unique spreading code, i.e., a code that spreads an original data-modulated carrier over a wide portion of the frequency spectrum in which the communications system operates.
Hybrid TDMA/CDMA systems have been proposed. Examples of such systems are described in U.S. Pat. No. 5,790,549 to Dent (issued Aug. 4, 1998), U.S. Pat. No. 5,566,168 to Dent (issued Oct. 15, 1996), U.S. Pat. 5,539,730 to Dent (issued Jul. 23, 1996), U.S. Pat. No. 5,481,533 to Honig et al. (issued Jan. 2, 1996) and in the “Draft PCS2000 Standard (PN-3390),” offered to the Joint Technical Committee on Wireless Access JCT(Air) by the Technical Ad Hoc Group (TAG) One (Omnipoint Corporation), Oct. 31, 1994.
Recently, wireless communications systems have seen a rapidly increasing demand for services other than transmission, including, for example, text messaging and multimedia services such as internet access, video and the like. Each of these services typically has different performance requirements. As it would generally be impractical to provide separate wireless infrastructures for each of these services, there is a need for wireless communications apparatus and methods whereby multiple services with differing performance requirements can utilize a common infrastructure in an effective and efficient manner.
SUMMARY OF THE INVENTION
According to the present invention, a terminal is assigned to an entire time slot or to a subchannel of a time slot defined by a spreading code based on one or more communications constraints associated with the terminal, e.g., based on a performance requirement, such as information rate or bit error rate, associated with the terminal, and a signal reception condition, such a signal to noise ratio, under which the terminal is operating. According to an aspect of the present invention, this assignment is performed such that system resources, such as the number of available time slots, available bandwidth, available spreading codes, and transmit power are optimized. In this manner, multiple services having varying performance requirements can be efficiently served by a common wireless infrastructure.
In particular, according to an aspect of the present invention, a wireless communications system including at least one base station operative to communicate on a plurality of carrier frequencies in repetitive time slots defined thereon is operated by assigning an entire time slot or a spreading-code defined subchannel of a time slot to a terminal based on a communications constraint associated with the terminal. The communications constraint may include a performance requirement, such as an information rate or an error rate, and a signal reception condition, such as signal to noise ratio.
According to an embodiment of the present invention, a single terminal is identified and a communications constra
Dent Paul W.
Koorapaty Havish
Wang Yi-Pin Eric
Ericsson Inc.
Myers Bigel & Sibley & Sajovec
Rampuria Sharad
Trost William
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