Multiplex communications – Wide area network – Packet switching
Patent
1992-05-18
1994-04-26
Chin, Wellington
Multiplex communications
Wide area network
Packet switching
370 20, 370 691, 375 1, H04B 7216, H04L 2728
Patent
active
053073410
DESCRIPTION:
BRIEF SUMMARY
This invention is described in the following statement:
The present invention relates to multiple access schemes for use in telecommunications. For example, the invention is applicable to satellite communications, cellular mobile communications, private mobile radio and other applications where packetised digital voice or data messages are to be communicated over a limited bandwidth which is available to a plurality of users.
1.0 BACKGROUND OF INVENTION
Previous multiple access schemes for satellite communications have operated on a variety of bases. One type is where resources are assigned by some control centre on a demand basis, such as Time Division Multiple Access (TDMA).
Other systems include variants of Code Division Multiple Access (CDMA), including Frequency Hopped Code Division Multiple Access (FH-CDMA) and Direct Sequence Code Division Multiple Access (DS-CDMA). Both these systems use spread spectrum transmission techniques. In FH-CDMA, user signatures occupy a time varying narrow band, while in DS-CDMA signatures occupy the full bandwidth.
In FH-CDMA, each user modulates a hopping carrier over the full transmission bandwidth. Special sequences are used to minimise hits between hopping patterns of different users. The number of carriers available is B/H, where B is the available bandwidth to be shared and H is the hopping rate. In FH-CDMA only one carrier frequency is transmitted per time interval.
In DS-CDMA a modulated carrier is multiplied by a high symbol rate frequency spreading signal, which is usually a pseudo random binary sequence. At the receiver the "despreading" operation is performed by multiplying the received signal with a locally generated version of the original spreading signal.
U.S. Pat. No. 3,292,179 to Magnuski discloses a system which utilises a fixed range of frequencies and time shifts to address users. It does not provide an interleaved frequency system in which address and data are comprised in a single transmission.
It is the object of the present invention to provide an improved multiple user communications system, particularly but not exclusively for satellite communications, which ameliorates at least some of the deficiencies of the prior art.
2.0 SUMMARY OF INVENTION
The present invention according to one aspect relates to a system which may be described as Frequency Comb Multiple Access (FCMA). In FCMA, user signatures interleave each other as "combs" of frequencies, spread over the available bandwidth. This arrangement enables both data and address information to be contained in a single transmission or energy burst.
According to a further aspect the invention provides a coding structure to minimise overlap between user signatures and hence errors between different users.
The present invention further provides apparatus for transmitting and receiving FCMA transmissions.
The general concept of FCMA relates to a system in which many users share a common channel, which may be a bus, satellite channel, or other resource. Each user (or group of users) is identified by one or more blocks of M=2.sup.k signatures, where k is an integer representing the number of bits transmitted per symbol. Each signature consists of a set of n specific frequencies drawn from a pool of size N=WR, where W is the available bandwidth of the common channel and R is the symbol rate at which communication occurs. By mutual agreement (prearranged), each signature corresponds to a specific bit pattern.
An exemplary system operates as follows: "To communicate with user y, user x sends a sequence of signatures representing the data being transmitted, from the block of signatures assigned to y. User y receives the information by monitoring the channel for signatures from its block.
When multiple users are simultaneously communicating with each other such that each user belongs to a single communications pair, then in the absence of noise, each transmitted signature will be reliably received. However the combination of frequencies representing the summation of all signatures being transmitted,
REFERENCES:
patent: 3197563 (1965-07-01), Hamsher
patent: 3872255 (1975-03-01), Nance
patent: 4189677 (1980-02-01), Cooper
patent: 4567588 (1986-01-01), Jerrim
patent: 4688210 (1987-08-01), Eizenhofer et al.
patent: 5103459 (1992-04-01), Gilhousen et al.
Boreli Roksana
Percival Terence M. P.
Simington Richard A. Z.
Stevenson Terence J.
Yates Kenneth W.
Chin Wellington
OTC Limited
University of Technology Sydney
LandOfFree
Random access multiple user communication system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Random access multiple user communication system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Random access multiple user communication system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1717369