Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1997-12-02
2001-07-17
Pham, Chi H. (Department: 2731)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S337000
Reexamination Certificate
active
06262980
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
The subject matter of the present application is related to the subject matter of U.S. patent application Ser. No. 08/775,466 entitled “Method and Apparatus for Providing High Speed Services Using a Wireless Communications System” to Thomas K. Fong, Paul Shala Henry,Kin K. Leung, Xiaoxin Qiu, Nemmara K. Shankaranarayanan and assigned to AT&T Corp., filed on Dec. 30, 1996 and U.S. patent application Ser. No. 08/832,546 entitled “Method and Apparatus for Resource Assignment in a Wireless Communications System” to Xiaoxin Qiu Kapil Chawla, filed Apr. 3, 1997, the entire disclosures of which are hereby incorporated by reference.
FIELD OF THE INVENTION
The invention relates to wireless communications systems. More particularly, the invention relates to a method and apparatus for dynamic resource allocation for broadband services in a wireless communications system.
BACKGROUND OF THE INVENTION
The need for high-speed broadband packet services will grow tremendously as telecommuting and Internet access become increasingly popular. Customers will expect high quality, reliable access to high-speed communications from homes and small businesses in order to, for example, access: (a) the World Wide Web for information and entertainment; (b) office equipment and data from home at rates comparable to Local Area Networks (LANs); and (c) multimedia services such as voice, image and video. Although varying with application, effective broadband communication requires a bandwidth sufficient to permit a data rate up to the range of several tens of Mega-bits per second (Mbps).
Traditional wireless communications systems have a problem delivering high-speed services because of the amount of bandwidth these services require. Bandwidth is a key limiting factor in determining the amount of information a system can transmit to a user at any one time. In terms of wireless networks, bandwidth refers to the difference between the two limiting frequencies of a band expressed in Hertz (Hz).
The concept of bandwidth may be better understood using an analogy. If information carried by a network were water, and links between communication sites were pipes, the amount of water (i.e., information) a network could transmit from one site to another site would be limited by the speed of the water and the diameter of the pipes carrying the water. The larger the diameter of the pipe, the more water (i.e., information) can be transmitted from one site to another in a given time interval. Likewise, the more bandwidth a communications system has available to it, the more information it can carry.
Traditional wired communications systems using modems and a physical transmission medium, such as twisted pair copper wire, cannot currently achieve the data rates necessary to deliver high-speed service due to bandwidth limitations (i.e., small pipes). Promising wired-network technologies for broadband access, such as Asymmetrical Digital Subscriber Loop (ADSL) and Hybrid Fiber-Coax (HFC), can be expensive and time consuming to install.
The benefit of wireless systems for delivering high-speed services is that they can be deployed rapidly without installation of local wired distribution networks. However, traditional wireless systems such as narrowband cellular and Personal Communications Services (PCS) are bandwidth limited. As an alternative, wireless solutions such as Multichannel Multipoint Distribution Service (MMDS) and Local Multichannel Distribution Service (LMDS) have become attractive, but these solutions presently offer limited uplink channel capacity and may not be capable of supporting a large number of users.
One solution for solving the bandwidth limitation problem for wireless systems is to maximize the available bandwidth through frequency reuse. Frequency reuse refers to reusing a common frequency band in different cells within the system. Refer, for example, to
FIG. 1
which shows a typical wireless communication system. A Base Station (BS)
20
communicate with several Terminal Stations (TS)
22
. The BS
20
is usually connected to a fixed network
24
, such as the Public Switched Telephone Network (PSTN) or the Internet. The BS
20
could also be connected to other base stations, or a Mobile Telephone Switching Office (MTSO) in the case of a mobile system. Each TS
22
can be either fixed or mobile.
The BS
20
communicates information to each TS
22
using radio signals transmitted over a range of carrier frequencies. Frequencies represent a finite natural resource, and are in extremely high demand. Moreover, frequencies are heavily regulated by both Federal and State governments. Consequently, each cellular system has access to a very limited number of frequencies. Accordingly, wireless systems attempt to reuse frequencies in as many geographic areas as possible.
To accomplish this, a cellular system uses a frequency reuse pattern. A major factor designing a frequency reuse pattern is the attempt to maximize system capacity while maintaining an acceptable Signal-to-Interference Ratio (SIR). SIR refers to the ratio of the level of the received desired signal to the level of the received undesired signal. Co-channel interference is interference due to the common use of the same frequency band by two different cells.
To determine frequency reuse, a cellular system takes the total frequency spectrum allotted to the system and divides it into a set of smaller frequency bands. A cellular communications system has a number of communications sites located throughout a geographic coverage area serviced by the system. The geographic area is organized into cells and/or sectors, with each cell typically containing a plurality of communications, sites such is a base station and terminal stations. A cell can be any number of shapes, such as a hexagon. Groups of cells can be formed, with each cell in the group using a different frequency band. The groups are repeated to cover the entire service area. Thus, in essence, the frequency reuse pattern represents the geographic distance between cells using the same frequency bands. The goal of a frequency reuse pattern is to keep co-channel interference below a given threshold and ensure successful signal reception.
The most aggressive frequency reuse pattern is where the same frequency band is use in every cell. One example of such a system is Code Division Multiple Access (CDMA) systems, which spread the transmitted signal across a wide frequency band using a code. The same code is used to recover the transmitted signal by the CDMA receiver. Although CDMA systems reuse the same frequencies from cell to cell, they require a large amount of frequency spectrum. In fact, the amount of spectrum required by CDMA systems to offer high-speed broadband services to a large number of users is commercially unrealistic.
Another example for aggressive frequency reuse Time Division Multiple Access (TDMA) systems, an example of which is discussed in U.S. Pat. No. 5,355,367, which use the redundant transmission of information packets to ensure an adequate SIR. The of redundant packet transmissions, however, merely trades one inefficiency for another. Although a frequency band can be reused from cell to cell, redundant packet transmission means that a smaller portion of that frequency band is now available for use by each cell in the system since multiple packets are required to ensure the successful reception of a single packet.
In addition to the frequency reuse problem, traditional cellular systems, are not engineered to allow a communications site to use the entire bandwidth available to the system (or “total system bandwidth”). Rather, traditional cellular systems employ various techniques in both frequency domain and time domain to maximize the number of users capable of being serviced by the system. These techniques are predicated on allocating smaller portions of the total system bandwidth to service individual communication sites. These smaller portions are incapable of providing sufficient bandwidth to offer high speed services.
An example
Leung Kin K.
Srivastava Arty
AT&T Corp
Pham Brenda H.
Pham Chi H.
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