Pulse or digital communications – Systems using alternating or pulsating current – Plural channels for transmission of a single pulse train
Reexamination Certificate
1998-04-28
2001-03-06
Pham, Chi (Department: 2631)
Pulse or digital communications
Systems using alternating or pulsating current
Plural channels for transmission of a single pulse train
C375S267000, C375S299000, C714S755000
Reexamination Certificate
active
06198775
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of communications an more particularly to diversity transmission systems and methods.
BACKGROUND OF THE INVENTION
Cellular communications systems are commonly employed to provide voice and data communications to a plurality of mobile units or subscribers. Analog cellular systems, such as designated AMPS, ETACS, NMT-450, and NMT-900, have been deployed successfully throughout the world. More recently, digital cellular systems such as designated IS-54B and IS-136 in North America and the pan-European GSM system have been introduced. These systems, and others, are described, for example, in the book titled
Cellular Radio Systems
by Balston, et al., published by Artech House, Norwood, Mass., 1993.
Frequency reuse is commonly employed in cellular technology wherein groups of frequencies are allocated for use in regions of limited geographic coverage known as cells. Cells containing equivalent groups of frequencies are geographically separated to allow mobile units in different cells to simultaneously use the same frequency without interfering with each other. By so doing many thousands of subscribers may be served by a system of only several hundred frequencies.
In the United States, for example, Federal authorities have allocated to cellular communications a block of the UHF frequency spectrum further subdivided into pairs of narrow frequency bands called channels. Channel pairing results from the frequency duplex arrangement wherein the transmit and receive frequencies in each pair are offset by 45 MHz. At present there are 832, 30-KHz wide, radio channels allocated to cellular mobile communications in the United States. To address the capacity limitations of this analog system a digital transmission standard has been provided, designated IS-54B, wherein these frequency channels are further subdivided into time slots. The division of a frequency into a plurality of time slots wherein a channel is defined by a frequency and a time slot is known as time division multiple access (TDMA).
As illustrated in
FIG. 1
, a cellular communication system
20
as in the prior art includes one or more mobile stations or units
21
, one or more base stations
23
and a mobile telephone switching office (MTSO)
25
. Although only three cells
36
are shown in
FIG. 1
, a typical cellular network may comprise hundreds of base stations, thousands of mobile stations and more than one MTSO. Each cell will have allocated to it one or more dedicated control channels and one or more voice channels. A typical cell may have, for example, one control channel, and 21 voice/data, or traffic, channels. The control channel is a dedicated channel used for transmitting cell identification and paging information. The traffic channels carry the voice and data information.
The MTSO
25
is the central coordinating element of the overall cellular network
20
. It typically includes a cellular processor
28
, a cellular switch
29
and also provides the interface to the public switched telephone network (PSTN)
30
. Through the cellular network
20
, a duplex radio communication link
32
may be effected between two mobile stations
21
or, between a mobile station
21
and a landline telephone user
33
. The function of the base station
23
is commonly to handle the radio communication with the mobile station
21
. In this capacity, the base station
23
functions chiefly as a relay station for data and voice signals. The base station
23
also supervises the quality of the link
32
and monitors the received signal strength from the mobile station
21
.
In a mobile communications system, signal performance my be reduced due to signal fading occurring as a result of physical interference and motion of the mobile user terminal. Fading can be reduced, for example, by increasing transmitter power, antenna size, and antenna height. These solutions, however, may be impractical and/or costly.
Accordingly, multiple transmit antennas have been used to provide transmission diversity as discussed for example in the reference by Guey et al. entitled “Signal Design for Transmission Diversity Wireless Communication Systems Over Rayleigh Fading Channels.” (Proceedings IEEE VTC, 1996). The disclosure of this reference is hereby incorporated herein in its entirety by reference. If the antennas are placed far apart, each signal will experience independent fading. This diversity can be made accessible to the receiver by switching between the transmitters at different time instants. The peak to average power ratio of the transmitted signal may be greatly increased, however, and the output amplifier design may be complicated.
Other transmission diversity techniques that do not switch between transmitters are ones using an intentional time offset or frequency offset, phase sweeping, frequency hopping, and/or modulation diversity. Most of these techniques use phase or frequency modulation of each transmitter carrier to induce intentional time-varying fading at the receiver. In addition, coded modulation schemes have been proposed to access the diversity of a multiple transmitter system without using an interleaver.
Notwithstanding the transmission diversity techniques discussed above, there continues to exist a need in the art for improved diversity methods, systems, and terminals.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide improved communications methods, systems, and terminals.
It is another object of the present invention to provide methods, systems, and terminals having improved transmission and reception.
These and other objects are provided according to the present invention by methods and systems wherein an information word from an information word set is mapped to first and second code words and transmitted. More particularly, the information word is mapped using first and second mapping functions defined such that each of the information words of the information word set is mapped to two different code words thus providing scrambling transmission diversity. The two different code words can then be received and decoded jointly to provide an estimate of the information word.
The scrambling transmission diversity according to the present invention thus provides that all information words are scrambled into two distinct code words from the code word set. Enhanced transmission and reception are thus provided for all information words. By using scrambling transmission diversity according to the present invention in a communications system with mobile user terminals such as a cellular communications system, most of the additional functionality can be added at the base station transmitters. Accordingly, little additional functionality is required at the mobile terminals where size and power considerations may be more constraining.
A method according to the present invention provides that an information word is mapped to first and second code words using first and second mapping functions. In particular, the information word is selected from a set of information words with each of the information words in the information word set having a first predetermined length. Moreover, the first and second code words are selected from a code word set with each of the code words in the set having a second predetermined length greater than the first predetermined length. The first and second mapping functions are defined such that each of the information words of the information word set are mapped to two different code words of the code word set. The first and second code words are then transmitted.
More particularly, the first and second code words can be transmitted from first and second spaced apart antennas. The first and second code words can be transmitted concurrently over a common frequency. Accordingly, the first and second code words can be transmitted without impacting the transmission capacity.
The first mapping function can include a first generator matrix wherein the first code word is equal to the first generator matrix
Khayrallah Ali S.
Ramesh Rajaram
Zangi Kambiz C.
Bayard Emmanuel
Ericsson Inc.
Myers Bigel & Sibley & Sajovec
Pham Chi
LandOfFree
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