The present invention relates to communications methods and systems (apparatus), and more particularly to methods and systems for allocating resources in wireless communications.
Wireless communications systems are commonly employed to provide voice and/or data communications to subscriber stations. 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 subscriber stations such as radiotelephones 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/or data information. Through the cellular network 20, a duplex radio communication link may be established between two radiotelephones 22 or between a radiotelephone 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 radiotelephones 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 subscriber stations such as satellite radiotelephones 23. The satellite conveys radiotelephone communications over duplex links 46 to satellite radiotelephones 23 and an earth station 44. The earth station 44 may in turn be connected to a PSTN 34, allowing communications between satellite radiotelephones, and communications between satellite radiotelephones 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. These access techniques include Frequency Division Multiple Access (FDMA) technology (e.g., the advanced mobile phone service (AMPS) standard); Time Division Multiple Access (TDMA) technology (e.g., the Telecommunication Industry Association (TIA)/Electronic Industries Association (EIA) 136 or digital AMPS (DAMPS) standard or the global system for mobile communication (GSM) standard); or Code Division Multiple Access (CDMA) technology (e.g., the TIA interim standard (IS) 95). The FDMA and TDMA technologies will be discussed in more detail hereafter.
Traditional analog cellular systems generally use FDMA to create communications channels. Radiotelephone communications signals are generally modulated waveforms that are communicated over predetermined frequency bands in a spectrum of carrier frequencies. In a typical FDMA system, each of these discrete frequency bands may serve as a channel over which cellular radiotelephones communicate with a base station or satellite serving a cell.
As the number of subscribers in a cellular radiotelephone system increases, the available frequency spectrum may need to be managed with greater efficiency to provide more channels while maintaining communications quality. This challenge may be further complicated because subscriber stations may not be uniformly distributed among cells in the system. More channels may be needed for particular cells to handle potentially higher local subscriber station densities at any given time. For example, a cell in an urban area might contain hundreds or thousands of subscriber stations at certain times, which may exhaust the number of channels available in the cell.
To provide service to increasing numbers of subscriber stations, conventional cellular systems may implement frequency reuse to increase channel capacity in each cell and increase spectral efficiency. More specifically, frequency bands may be allocated to each cell such that cells using the same frequencies are geographically separated to allow subscriber stations in different cells to use the same frequency simultaneously without interfering with each other. Accordingly, for example, many thousands of subscriber stations may be served by a system having only several hundred allocated frequency bands.
Another technology that may further increase channel capacity and spectral efficiency is TDMA. A TDMA system may be implemented by subdividing the frequency bands used in conventional FDMA systems into sequential time slots. Communication over a frequency band typically occurs via a repetitive TDMA frame structure wherein each frame includes a plurality of time slots, also referred to herein as sub-periods. Each subscriber station communicates with the base station using bursts of digital data transmitted during the subscriber station's assigned time slots.
A channel in a TDMA system may include at least one time slot on at least one frequency band, and typically includes at least one time slot in each of a plurality of frames. As discussed in the foregoing, channels may be used to communicate voice, data, and/or other information between users, e.g., between a subscriber station and a wireline telephone.
CDMA systems, such as those conforming to the IS-95 standard, can 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.
The subscriber stations may include traditional radiotelephones or mobile terminals. These devices may include a serial data port in which a device, such as a computer or Personal Digital Assistant (PDA), may be connected to establish a wireless data connection. The subscriber stations also may include such wireless communications devices which are being used for voice calls, data calls, facsimile transfer, Internet access, paging, and other personal organization features such as calendar management or even travel directions via the Global Positioning System (GPS). These devices may include a cellular radiotelephone with a multi-line display, a Personal Communications System (PCS) terminal that may combine a cellular radiotelephone with data processing, facsimile and data communications capabilities, a PDA that can include a radiotelephone, pager, Interet/intranet access, Web browser, organizer, calendar and/or a GPS receiver, and conventional laptop and/or palmtop receivers that include radiotelephone transceivers. These devices also may be referred to as “pervasive computing” devices. As used herein, the term “subscriber stations” includes all of these radiotelephones, mobile terminals, wireless communicators, personal communications systems, pervasive computing devices and/or other fixed or mobile wireless communications receivers.