Multiplex communications – Communication over free space – Using trunking
Reexamination Certificate
2000-03-30
2002-12-10
Olms, Douglas (Department: 2732)
Multiplex communications
Communication over free space
Using trunking
C370S329000, C370S332000, C370S437000
Reexamination Certificate
active
06493331
ABSTRACT:
BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention relates to data communication. More particularly, the present invention relates to a novel and improved method and apparatus for controlling transmissions of a communications system to increase efficiency and improve performance.
II. Description of the Related Art
Wireless communications systems are becoming more prevalent as the systems of choice for supporting a variety of communications applications. One such wireless communications system is a code division multiple access (CDMA) system that facilitates communication among a large number of system users. Other wireless communications systems include a time division multiple access (TDMA) system and a frequency division multiple access (FDMA) system. A Global System for Mobile (GSM) communications system is a TDMA-based system widely employed in Europe.
The spread spectrum modulation technique of CDMA has significant advantages over other modulation techniques for multiple access communications systems. The use of CDMA techniques in a multiple access communications system is disclosed in U.S. Pat. No. 4,901,307, entitled “SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS,” issued Feb. 13, 1990, and U.S. Pat. No. 5,103,459, entitled “SYSTEM AND METHOD FOR GENERATING SIGNAL WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM,” issued Apr. 7, 1992, both assigned to the assignee of the present invention and incorporated herein by reference.
CDMA systems are typically designed to conform to one or more CDMA standards. Examples of such CDMA standards include the “TIA/EIA/IS-95-A Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System” and the “TIA/EIA/IS-95-B Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System” (collectively, the IS-95 standard), the TIA/EIA/IS-98-A, -B, and -C standards entitled “Recommended Minimum Performance Standard for Dual-Mode Spread Spectrum Cellular and PCS Mobile Stations,” and “The cdma2000 ITU-R RTT Candidate Submission,” (hereinafter, the IS-2000 standard). New standards are continually proposed and adopted for use.
In a wireless communications system, communication between users is conducted through one or more base stations. A first user on one terminal (e.g., a remote station) communicates to a second user on a second terminal by transmitting data on an uplink to a base station. The base station receives the data and can route the data to another base station. The data is then transmitted on the downlink from the base station to the second terminal. The downlink refers to transmission from the base station to the terminal and the uplink refers to transmission from the terminal to the base station. In IS-95 systems, the uplink and the downlink are allocated separate frequencies.
In a wireless communications system, each transmitting source acts as potential interference to the receivers in the system. To combat the interference experienced by the terminals and base stations and to maintain a required level of performance, conventional TDMA and FDMA systems resort to frequency reuse techniques whereby not all time slots and frequency channels, respectively, are used in each cell. For example, a TDMA system may employ a 7-cell reuse pattern in which the total operating bandwidth W is divided into seven equal operating frequency bands (i.e., B =W/7) and each of the seven cells is assigned to one of the frequency bands. Thus, every seventh cell reuses the same frequency band. With reuse, the co-channel interference levels experienced in each cell are reduced relative to that if each cell is assigned the same frequency band. However, reuse patterns of more than one cell (such as the 7-cell reuse pattern for a conventional TDMA system) represent inefficient use of the available resources since each cell is allocated and able to use only a portion of the total operating bandwidth.
A CDMA system is capable of operating with a 1-cell reuse pattern (i.e., adjacent cells can use the same operating bandwidth). However, the CDMA system is designed to carry voice data having a low data rate (e.g., 32 kbps or less). Using code division spread spectrum, the low-rate data is spread over a wide (e.g., 1.2288 MHz) bandwidth. Because of the large spreading factor, the transmitted signal can be received at a low or negative carrier-to-noise-plus-interference (C/I) level, despread into a coherent signal, and processed. The CDMA system is not designed for data transmission at high data rates.
Given the ever-growing demand for wireless communication, method and apparatus that can support data transmission at high data rates and allow for better utilization of the available resources to increase efficiency and improve performance are highly desirable.
SUMMARY OF THE INVENTION
The present invention provides techniques for controlling transmissions of a communications system to increase efficiency and improve performance. A communications system is typically required to satisfy a particular coverage criteria typically defined by a specified minimum average bit rate being achieved for a prescribed percentage (e.g., 99.99%) of the time and/or a particular percentage (e.g., 99%) of the users with received signal levels exceeding a particular C/I threshold. The coverage requirement is often influenced by a small percentage of disadvantage users that experience excessive interference from a small number of interfering sources.
The invention recognizes this fact, and provides various techniques that attempt to assist disadvantage users when and where possible to achieve the coverage requirement. In accordance with certain aspects of the invention, each cell in the system can be designed to operate in accordance with a set of back-off factors that identify the reductions in peak transmit power levels for the channels associated with the back-off factors. The back-off factors are defined to provide the required power to a large percentage of the users while reducing the amount of interference.
In accordance with other aspects of the invention, the cells operate using an adaptive reuse scheme that allows the cells to efficiently allocate and reallocate the system resources to reflect changes in the communications system. A reuse scheme is initially defined and resources are allocated to the cells. During operation, changes in the operating conditions of the system are detected and the reuse scheme is redefined as necessary based on the detected changes. For example, the loading conditions of the cells can be detected, and the resources can be reallocated and/or the reuse scheme can be redefined based on the detected loading conditions.
In accordance with certain other aspects of the invention, techniques are provided to efficiently schedule data transmissions and to assign channels to users. Data transmissions can be scheduled based on user priorities, some fairness criteria, system requirements, and other factors. The data transmissions to the users are assigned to available channels based on a number of channel assignment schemes. Channel metrics are also provided, which can be used to prioritize users and for channel assignments. These various aspects of the invention are described in further detail below.
A specific embodiment of the invention provides a method for controlling transmissions in a communications system. In accordance with the method, the available system resources are first partitioned into a number of channels. One or more characteristics of the communications system are determined and a set of back-off factors is defined for the channels based on the determined system characteristics. Each channel is associated with a respective back-off factor, ranging from zero to one, that identifies a reduction from the peak transmit power level. Data transmissions are transmitted on the channels at power levels determined based on the back-off factors. One or more channels are typically associated with
Antonio Franklin P.
Holtzman Jack
Wallace Mark
Walton Jay R.
Baker Kent D.
Olms Douglas
Qualcomm Incorporated
Rouse Thomas R.
Sam Phirin
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