Patent Application
20070248043
Wireless frequency spectrum is controlled by government bodies. These government bodies allocate the frequency spectrum to particular wireless operators, and place conditions on how the frequency spectrum is used. For example, allocated frequency spectrum is typically required to operate either in a time division duplex (TDD) or frequency division duplex (FDD) mode. In a system that operates in a TDD mode, the uplink and downlink channels share the same frequency band, but are transmitted and received by the base station during mutually exclusive periods of time. In a system that operates in an FDD mode, the uplink and downlink channels are transmitted simultaneously on different frequency bands.
The 2.5 GHz frequency spectrum currently consists of TDD spectrum, and is being partially re-banded to support FDD. Currently, Code Division Multiple Access (CDMA) and the IEEE 802.16 standard, which uses Orthogonal Frequency Division Multiple Access (OFDMA), both support TDD and FDD modes. Typically, systems which use CDMA or the IEEE 802.16 standard operate in either a TDD or FDD mode.
Next-generation systems that will be deployed in the 2.5 GHz band for wireless broadband services must be flexible in spectrum utilization to maintain a low-cost base and support deployment under geographically varying spectrum positions. Ownership of the 2.5 GHz spectrum is fragmented, with many licensees owning small channels with a certain geographic limit. In order to minimize deployment cost and the cost of capacity growth, the next-generation technology deployed in this band must be flexible enough to support TDD, where a TDD spectrum is owned, to support FDD, where an FDD spectrum is owned, and to support a capacity growth plan that minimizes the cost of utilizing new pieces of spectrum that become available. However, current systems are designed in such a way that a base station supports only TDD or FDD operation.
The present invention provides a method, apparatus, and computer-readable medium for dynamically assigning radio resources between a frequency division duplexing (FDD) carrier and a time division duplexing (TDD) carrier. Simultaneous use of both TDD and FDD schemes can help significantly enhance the achieved capacity of the resources.
With FDD and TDD operating simultaneously with the same technology, the allocation of resources between the two modes becomes an issue. Exemplary embodiments of the present invention employ a single receive and transmit chain to reduce device cost and complexity. Such a device can only operate in either the TDD or the FDD mode at any instant. However, frequency selective fading, traffic load within the sector, and interference from surrounding sectors vary as a function of time, frequency, and device location. Therefore, to optimize the capacity of the two systems, exemplary embodiments of the present invention provide a smart resource allocation scheme that can dynamically assign resources on the two duplexing schemes is required.
This is a new problem introduced by the capability of certain air interface technologies to support both TDD and FDD modes of operation. This allows the technology to operate in spectrum that supports both types of duplexing schemes. Traditionally, spectrum allocations are clearly defined to be either TDD or FDD. As described above, the 2.5 GHz band is deviating from this approach, prompting new innovations to ensure the lowest-cost deployment approach.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.
In accordance with the present invention, devices are able to interoperate between TDD and FDD modes of operation and are able to receive or transmit in either mode. The interoperability can occur on a burst-by-burst basis, where a burst is a single unit of resource allocation. Exemplary embodiments of the present invention include a dynamic resource allocation scheme that will be able to assign radio resources dynamically to a device across the two duplexing schemes.
For a downlink resource assignment, a base station constantly monitors conditions of both TDD and FDD carriers, which can be provided by downlink measurements from devices operating on both carriers. For example, the radio frequency (RF) conditions and traffic load on the TDD and FDD carriers can be monitored. The RF conditions may include interference and channel fading, for example, and the traffic load can be an instantaneous load. The base station dynamically assigns radio resources to a user on either the TDD or FDD carrier, depending upon the monitored conditions. Similarly, for uplink resource assignment to individual devices, the base station can utilize measurements at its receiver on both carriers, and can assign resources to the device on the carrier with the best RF conditions and lightest traffic load, for example. In effect, the resource assignment with this scheme includes not only radio resources (such as CDMA codes or OFDMA sub-channels), but also RF carrier resources (TDD versus FDD). Resource assignments are signaled to the devices via the control channels or other messaging protocols/processes. The efficiency of switching between TDD and FDD operation will depend on the device processing power, the physical layer (PHY) and media access control (MAC) layer design of the air interface technology.
A significant advantage of this scheme is that the device can receive or transmit on the most optimal carrier, from an RF and traffic perspective, while minimizing the device transceiver complexity, by requiring a single RF transmit/receive chain.
The present invention encompasses the expanded case of multiple FDD and TDD carriers in a sector or site. Thus, although only one FDD carrier and one TDD carrier are illustrated in
In another exemplary embodiment of the present invention, a computer-readable medium encoded with a computer program for dynamically assigning radio resources between a frequency division duplexing (FDD) carrier and a time division duplexing (TDD) carrier is provided. The term “computer-readable medium” as used herein refers to any medium that participates in providing instructions for execution. Such a medium may take many forms, including but not limited to, non-volatile media, volatile media, and transmission media. Non-volatile media includes, for example, optical or magnetic disks. Volatile media includes, for example, dynamic memory. Transmission media includes coaxial cables, copper wire and fiber optics. Transmission media can also take the form of acoustic or light waves, such as those generated during radio-wave and infra-red data communications.
Common forms of computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, or any other magnetic medium, a CD-ROM, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, an EPROM, a FLASH-EPROM, any other memory chip or cartridge, a carrier wave, or any other medium from which a computer can read.
An exemplary embodiment of a computer-readable medium encoded with a computer program for dynamically assigning radio resources between a frequency division duplexing (FDD) carrier and a time division duplexing (TDD) carrier is illustrated in
Processor 335 is coupled to transmitter 315 and receiver 320, and includes logic 345, 350, 355, 360, and 365. Logic 345 can allocate a resource assignment for a downlink on an FDD carrier, logic 350 can allocate a resource assignment for an uplink on the FDD carrier, logic 355 can allocate a resource assignment for a downlink on a TDD carrier, and logic 360 can allocate a resource assignment for an uplink on the TDD carrier. Logic 365 can monitor RF conditions and traffic load of the TDD and FDD carriers. Processor 335 can be a microprocessor, field programmable gate array (FPGA), application specific integrated circuit (ASIC) and/or the like. Processor 335 is coupled to a memory 340. Memory 340 can be a random access memory (RAM), read only memory (ROM), flash memory, hard disk and/or the like. The operation of an exemplary base station is described above in connection with
The methods described above in connection with
While the invention has been described in connection with various embodiments, it will be understood that the invention is capable of further modifications. This application is intended to cover any variations, uses or adaptation of the invention following, in general, the principles of the invention, and including such departures from the present disclosure as, within the known and customary practice within the art to which the invention pertains.
The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.
